Select Committee on Treasury Eleventh Report

2  How the population is counted

What is being counted and how it is counted

8. The Statistics Authority (and previously the ONS) produces population estimates at national and local level. The most authoritative population estimates for the United Kingdom are derived from the Census of Population, which takes place every 10 years; the most recent one was held in April 2001. Population estimates from the Census are updated each year by the ONS to produce mid-year population estimates for the years between each Census.[8]

9. Current population statistics relate to the usually resident population; those statistics record people where they usually live.[9] The usually resident population does not always coincide with the number of persons to be found in an area at a particular time of the day or year. For example the day-time populations of city centres, such as London or Manchester, and the summertime populations of holiday resorts would normally be larger than their usually resident populations. The definition of the usually resident given in the 2001 Census was as follows:

The 2001 Census has been conducted on a resident basis. This means the statistics relate to where people usually live, as opposed to where they are on Census night. Students and schoolchildren studying away from home are counted as resident at their term-time address. As in 1981 and 1991, residents absent from home on Census night were required to be included on the Census form at their usual/resident address. Wholly absent households were legally required to complete a Census form on their return. No information is provided on people present but not usually resident.[10]

10. The ONS noted that "for most people, defining where they 'usually' live for the purposes of the Census is quite straightforward. However for a minority of people the concept of usual residence is more difficult and it may be difficult to apply a general rule as to where they should be assigned as 'usually' living".[11]

The role of the Census


11. The Census is a complete count of the population of the United Kingdom. It has been conducted every ten years[12] since 1801, with the exception of 1941 during the Second World War.[13] The 2001 Census cost approximately £255 million for the UK as a whole. The law requires every household to complete and return a Census form. [14] Professor David Martin, Chair of the Royal Statistical Society's Census Study Group, noted that:

The census continues to be essential to the creation of baseline population statistics and forms a foundation and reference point for alternative sources of population estimates. Due to its high population coverage, it is however unrivalled as a source of socio-economic population detail at small area level. While some of these topics are covered in greater detail by survey datasets, none offers any small area geography.[15]


12. The first known census was taken by the Babylonians, over 5000 years ago, in 3800 BC. Records suggest that it was taken every six or seven years and counted the number of people and livestock, as well as quantities of butter, honey, milk, wool and vegetables.[16] Censuses in Egypt are said to have been taken already during the early Pharaonic period, in 3340 BC and in 3050 BC. One of the earliest documented censuses was taken in 500-499 BC by the Persian Empire's army for issuing land grants, and for taxation purposes.[17] The Bible also relates accounts of several censuses. The Book of Numbers describes a divinely-mandated census that occurred when Moses led the Israelites from Egypt. A later census called by King David of Israel is referred to as the "numbering of the people". A Roman census is also mentioned in one of the best-known passages of the Bible in the Gospel of Luke.[18]

13. The best-known historical estimate of the British population was made in 1695 by Gregory King. It concluded that the population of England and Wales was 5.5 million. [19] In the 18th century there were widespread fears that a census could be used for taxation purposes. A Bill proposing "taking and registering an annual Account of the total Number of People, and of the total Number of Marriages, Births and Deaths; and also of the total Number of Poor receiving Alms from every Parish and extra-parochial Place in Great Britain" was passed by the House of Commons on the 8th May 1753. However, Mr Thornton, MP for York, did not accept that

that there was any set of men, or indeed, any individual of the human species so presumptuous and so abandoned as to make the proposal we have just heard ... I hold this project to be totally subversive of the last remains of English liberty. [20]

14. After the second reading in the Lords the Bill was referred to a committee, but the session ended before it was considered and so the Bill lapsed. The first census was held 48 years later, on 10 March 1801 by a house-to-house enquiry together with returns of baptisms and burials between 1700 and 1800, and marriages between 1754 and 1800 as supplied by the clergy. [21]


15. The Census gathers information on a wide range of subjects relating to the population such as age, sex, ethnic composition, education, socio-economic class, religion, housing, families, transport and work. It is designed to provide a complete picture of the nation, counting the numbers of people living in each city, town and country area. It provides data about each area and its population, including the proportion of young and old people, what jobs people do, and the type of housing they live in.[22]

16. Population estimates are available to the public and provide various estimates of the resident population for:

  • The UK as a whole and England, Wales, Scotland and Northern Ireland separately by sex and single year of age.
  • Government Office regions, counties, unitary authorities and local government districts in England and unitary authorities in Wales by sex and five-year age group or broad age group (children, working age and older people).
  • Health areas in England and Wales (strategic health authorities in England and local health boards in Wales) by sex and five-year age group or broad age group.
  • Legal marital status for England and Wales as a whole.[23]
  • Experimental population estimates for the very elderly, ethnic groups, parliamentary constituencies and Super Output Areas.


17. The United Nations Statistics Division issues standards and methods approved by the Statistical Commission to assist national statistical authorities and other producers of official statistics in planning and carrying out successful population and housing censuses.[24] The Census in the UK. is a national count of the population through the completion of Census forms delivered door to door.[25]

18. In 2001, the ONS employed enumerators (a person used to perform door-to-door delivery and collection of Census papers during the Census period). The enumeration of the 2001 Census was organised largely in the traditional way, with the delivery of the self-completion forms by enumerators to households and communal establishments prior to Census Day (29 April 2001). However, for the first time in a census in the UK, provision was made for these forms to be mailed back to local census management teams as the prime means of collection; only those households who had failed to return a form in this way were followed up by field staff.[26]

19. The Census in the United Kingdom consists of a complete enumeration of the population. Enumeration is not the only method used to take a national census. The Treasury Committee visited Sweden in November 2007 to discuss their method of calculating national statistics. Sweden uses a population register, which replaces a census and provides a snapshot of the population at any point in time and at any level of geographic detail.

20. Statistics Sweden has full access to administrative records maintained in government. Legislation allows these administrative records to be linked together for statistical purposes. Four linked registers have been developed from the sources available, namely registers of population, jobs, real estate and businesses. The population register holds only core details (name, address, sex, date and place of birth and a personal reference number) of every resident and provides the base for all public agencies' personal records. Its key feature is that a person's data held in separate administrative registers are assembled using the personal reference number in the population register for linking.

21. The statistical offices in Finland, Norway and Denmark also have the authority to link administrative records together for statistical purposes and the UK Statistics Commission noted that "it seems to be regarded as self evidently the most efficient way of putting together information that both government and public need."[27]


22. The Treasury Committee visited Dublin in 2007. During the visit the Committee met representatives from the Irish Central Statistics Office and discussed what lessons the UK could learn from the Irish Census. There had been a census in Ireland every five years from 1951 to 2006, with two exceptions: the 1976 census was cancelled, and the 2001 census, which was postponed until 2002 because of foot and mouth disease. There was strong support in Ireland for a five-yearly census, partly because Ireland had no population register.[28]

23. Professor David Martin thought that "an increased frequency of census would be useful to researchers and planners, especially with regard to population characteristics which are known to change quite rapidly, such as the ethnic composition of the population". He commented that researchers would prefer population data more frequently but would accept the continuation of a decennial census "providing it is sufficiently resourced to produce outputs of the absolutely highest quality, allowing it to continue to be used as the key reference dataset".[29]


24. The 2001 Census was completed on Sunday 29 April 2001. It covered an estimated fifty nine million people in thirty three million households, asking 41 questions.[30] The Census form was also produced in Welsh and there was one extra question in Wales about the use of the Welsh language. By comparison the first Census held in 1801 asked only five questions of ten million people in two million households.[31]

25. The next full census of England and Wales will take place in 2011. Before the Census is held, a detailed planning programme is being undertaken, the 2011 Census Project. The Project is designed to determine what information will be gathered, how it will be captured, how it will be processed and how the results will be produced and delivered. It is proposed that pre-addressed questionnaires will be posted out to most households using national address lists.

26. A test of current proposals for the 2011 Census was held in England and Wales on 13 May 2007. The 2007 Census Test aimed to assess new questions that could be incorporated into the Census as well as innovations in the design of the Census form, the effectiveness of different enumeration approaches (for example postal returns and face-to-face interviews), and methods of working with Local Authorities to improve the enumeration process (particularly in 'hard-to-count' areas). The Test was conducted on a voluntary basis in five Local Authority areas, namely Liverpool, Camden, Bath and North East Somerset, Carmarthenshire and Stoke-on-Trent.[32]

27. A full rehearsal of the systems designed for the 2011 Census will be take place in 2009. A variety of enumeration strategies will be tested to address coverage in hard-to-count groups. These will include hand-delivery of forms and increased enumeration resources in the most difficult areas.[33]

Mid-year population estimates


28. The ONS publishes mid-year population estimates annually for England and Wales.[34] Mid-year population estimates establish the population usually resident on 30 June of each year. The national population projections are based on the estimated mid-year population and assumptions on future levels in fertility, mortality and migration.


29. Estimates are calculated from the population data in the previous year using the cohort-component methodology. This population is "aged on" by one year (for example all eight-year-olds become nine-year-olds one year later). Those who were born during the 12 month period are then added on to the population and all those who have died during the 12 month period are removed. Births and deaths data used in the compilation of mid-year population estimates are obtained from General Register Offices through the compulsory registrations of all births and deaths occurring in England and Wales, Scotland and Northern Ireland.[35]

30. The other factor to be taken into account in estimating the national population is the movement of people in and out of the UK (international migration). An international migrant is defined as a person who changes his or her country of residence for a period of at least a year. When estimating the population of different areas of the UK, movements within the UK (internal migration) also need to be taken into consideration. Internal migration includes both cross-border moves between the four constituent countries of the UK and moves between local areas within each part of the UK.

31. ONS reported that it is continually researching ways of ensuring and improving the quality of the population estimates.[36] Mid-2006 population estimates for the UK were published by ONS on 22 August 2007. The 2006 estimates incorporate improvements in the estimation of international migration and, as a result, population estimates for 2002 to 2005 have also been revised.[37]

Mid-year population estimates methodology

Estimated resident population at time T

Natural Change - add births, subtract deaths

International Migration - add inflows, subtract outflows

Internal migration - add inflows, subtract outflows

Special Populations - UK armed forces, foreign armed forces and dependants, prisoners and school boarders

Estimated resident population at time T + 1

Source: Office for National Statistics memorandum

Data used in the mid-year estimates


32. It is compulsory to register all births and deaths within the United Kingdom. The General Register Office collects this data. The ONS noted that this information provided a reliable indication of these events.[38]


33. Mid-year estimates are calculated using estimates of both international and internal migration. Within this Report, we discuss international migration as the flows of international migrants to and from the United Kingdom, and internal migration as the movement of people within the United Kingdom from one area of the country to another. Migration is the most difficult part of the population estimate process, as migratory moves are not registered in the UK, either at the national or local level. The best proxy data[39] available on a nationally consistent basis are used to calculate estimates of migration. Mr Blake-Herbert, Director of Finance, Slough Borough Council told the Sub-Committee that it did not matter to Local Authorities "whether someone has come from Poland or [moved] from Putney to Slough" if the statistics were not able to track them. [40]

34. International migration describes both emigration (the act of leaving one's country to settle in another) and immigration (the act of arriving settling in another country). The Statistics Commission reporting on the 2001 Census commented that:

methods currently used for measuring migration into and out of the UK, and between Local Authority areas, are unreliable. Particularly unreliable are the estimates of international emigration and immigration into and out of Central London. Without improved methods, up-dating population census figures is liable to error.[41]

Ms Karen Dunnell, the National Statistician, told the Sub-Committee that she "had a task force looking at migration data… particularly for reliable figures on emigration".[42]


35. The ONS annual publication, International Migration, presents a range of statistics on flows of international migrants to and from the United Kingdom since 1991.[43] The publication uses three main sources of data: the International Passenger Survey; Home Office data on asylum seekers and persons entering the UK as short-term visitors but who were subsequently granted an extension of stay for a year or longer for other reasons (e.g. as asylum seekers, students, or on the basis of marriage); and estimates of migration between the UK and the Irish Republic (using information from the Irish Quarterly National Household Survey and the National Health Service Central Register).

36. The Sub-Committee was told that international migration was one of the most difficult components of population change to measure accurately. Considerable numbers of people travel into and out of the United Kingdom each year. There is no single, comprehensive data source that is able to provide the information, at national and local levels, required for statistical purposes.[44]


37. The International Passenger Survey (IPS) is a survey of a random sample of passengers entering and leaving the UK. The ONS estimates that over a quarter of million face-to-face interviews are carried out each year with passengers entering and leaving the UK through the main airports, seaports and the Channel Tunnel.[45] The survey was originally designed to provide data primarily for tourism and business travel purposes, to inform the travel account of the balance of payments, but is now also used by the ONS to estimate international migration.[46]

Methodology of the International Passenger Survey

Interview teams are required to identify every 'nth' person ('n' varies by port and route, taking account of traffic flows) in the flow of passengers past a specified point. Information is collected from any migrants identified through these routine samples. However, for selected ports and routes, additional passengers are selected for a short interview.

The questions asked are designed to establish whether the people selected are migrants. If this is the case, more detailed questions are then asked. Prior to 2007, these additional interviews were carried out only for arrivals (to identify immigrants only). The ONS has reported that since January, they have been extended to departures (to boost the number of emigrants interviewed). At present the only reliable source of information on emigration is the IPS.

Sampling for the International Passenger Survey is carried out at all airports with more than 1 million international passengers travelling through them. This currently includes 5 London airports, Manchester and 10 regional airports. The IPS uses data provided by the Civil Aviation Authority (CAA) to extrapolate the sample figures to total flows, to ensure that all people are accounted for. In addition the Channel Tunnel and 10 sea ports are covered and again the survey data are weighted to total flows supplied by Euro tunnel, Eurostar and Department for Transport.


38. Internal migration data is based on patient register and patient re-registration recorded in the National Health Service Central Register (NHSCR) and shows moves between Local Authorities, Government Regions in England and Wales only. It does not include the rest of the UK (Scotland and Northern Ireland).[47] From the mid-1999 population estimate onwards, data from General Practitioner (GP) patient records have been used to estimate flows of internal migrants between areas within England and Wales. Every health authority in England and Wales holds a register of the patients registered with GPs within their area of responsibility. This contains each patient's NHS number, date of birth, sex and postcode. The ONS downloads data from health authorities registers each year. The ONS combines the data to create a total patient register for the whole of England and Wales.[48]

39. An internal migrant is defined as a person who, between one year and the next, changes their area of residence. Comparing records in one year with those of the previous year enables identification of people who change their postcode. This method of comparing registers at two snapshots in time can miss certain groups of people who do not appear on the patient registers in two consecutive years (births, deaths, those joining or leaving the armed forces or entering or leaving the UK). To overcome this the estimates of the number of migrants from the patient register are only captured on the National Health Service Central Register (NHSCR), which measures moves between such health authorities but has the benefit of being constantly updated. By combining the two data sources, ONS produces an estimate of internal migration.[49]

Current role of administrative data


40. National Insurance Numbers are issued by the Department for Work and Pensions to individuals when they reach age 16 and are used to record a person's National Insurance contributions and social security benefit claims. New numbers are issued to all non-UK born nationals aged 16 or over working, planning to work or claim benefits legally in the UK, regardless of how long individuals intend to stay.

41. The following are excluded:

42. This register provides numbers registering for a National Insurance Number. There is no requirement to de-register on leaving the country. Therefore the figures do not show the number of foreign nationals working or claiming benefit at any given point nor do they distinguish between long and short term migrants. [51]


43. The School Census provides, every term, a snapshot of all school pupils in state education in England. It is collected by the Department for Children, Families and Schools and is used for monitoring the effectiveness of policies and school/Local Authority funding. Similar systems are in place in the devolved administrations. [52] The Higher Education Statistics Agency (HESA) collects data about students attending all publicly-funded higher education institutions in the UK. The term-time full postcode will be collected from 2007/08, thereby overcoming a limitation in the coverage of current data. This will inform estimates both of internal migration of students and international migration of foreign students in higher education.[53]

Migrant registration

44. Nationals of countries (other than Cyprus and Malta) that joined the EU in May 2004—the A8 countries—who wish to take up employment in the UK for a period of at least a month are generally required to register with the Worker Registration Scheme (WRS). [54]Workers who are self-employed do not need to register. They must register more than once if they are employed by more than one employer and must re-register if they change employer. Each application represents one job, not one applicant. [55]

45. The population covered on the WRS includes:

  • Long-term international migrants from A8 countries working as employees in the UK;
  • Visitors and short term migrants from A8 countries, staying for over a month, and intending to work as employees in the UK; and
  • Dependants of WRS applicants. It is likely that there is some double counting as dependants may also be registered in their own right on the WRS. [56]

46. The following are excluded:

  • Migrants from A8 countries who are self employed;
  • A8 migrants staying for less than a month;
  • A8 migrants who migrate or visit the UK for reasons other than work, for example including potentially many students;
  • Migrants from non-A8 countries. [57]

47. Figures relate to the address of the applicant's employer rather than their own usual residence and are produced by date of application rather than date of entry into the UK. The data only include those registering when they take up a job, when intended length of stay is recorded. However neither actual duration of employment or whether the applicant returns home are recorded. [58]

Meeting the needs of the user

48. The ONS argued that population and migration statistics were produced by combining the "best possible information currently available". They were produced to a "high quality standard, using internationally recognised and transparent methods that have been peer reviewed by external experts". [59] We recognise that in a period of significant population change and individual mobility meeting the requirements of users has become more complex for the Statistics Authority. The amount of population turnover, both nationally and locally has made it increasingly difficult for the current methods of counting the population to estimate the numbers of people in an area and on what basis they are there.

8   A short guide to population estimates, November 2004; National Statistics, Back

9   Ev 201 Back

10   A short guide to population estimates, November 2004; National Statistics, Back

11   IbidBack

12   This is In line with guidance issued by the United Nations Statistics Division, Principles and Recommendations for Population and Housing Censuses, Rev.2 2008 Back

13   200 years of the Census, Office for National Statistics, Back

14   Why do we have a Census, National Statistics, Back

15   Ev 25 Back

16   History of the census, Statistics Canada,  Back

17   A. Kuhrt, The Ancient Near East c. 3000-330BC Vol 2 Routledge, (London 1995), p 695 Back

18   Raymond E. Brown, The Birth of the Messiah: A Commentary on the Infancy Narratives in Matthew and Luke, Anchor Bible; Updated edition (1999), p 413 Back

19   Why take a census, National Archives, Back

20   Ibid.  Back

21   Key dates in Census, statistics and registration, Great Britain 1000-1899, see  Back

22   Census background, National Statistics,  Back

23   Population Estimates for UK, England and Wales, Scotland and Northern Ireland, National Statistics, Back

24   Principles and Recommendations for Population and Housing Censuses, United Nations Statistics Division Rev.2 2008 Back

25   2010 World Population and Housing Census Programme, United Nations Statistics Division,  Back

26   2001 Census, definitions, para 2.5, National Statistics, Back

27   The Nordic Contrast: a paper by the Statistics Commission, September 2007 Back

28   History of Irish census records, National Archives of Ireland, Back

29   Ev 25 Back

30   Nine more questions than the 1991 Census. Back

31   200 years of the Census, Office for National Statistics, March 2001 Back

32   Ev 216-217 Back

33   The 2011 Census, National Statistics, Back

34   Making a Population Estimate in England and Wales, National Statistics, Back

35   A Short Guide to Population Estimates, National Statistics, November 2004 Back

36   Making a population estimate in England and Wales, ONS, August 2007 Back

37   Ev 205 Back

38   Ev 209  Back

39   Information of this kind is called "proxy data" because it is used in the place of actual data recording internal migration.  Back

40   Q 147 Back

41   The 2001 Census in Westminster: Interim Report, Statistics Commission, October 2003 Back

42   Q 193 Back

43   Ev 206 Back

44   IMPS Methodology, National Statistics, Back

45   International Passenger Survey, National Statistics, Back

46   Ev 207 Back

47   Ev 181 Back

48   Ev 208 Back

49   Ibid. Back

50   Ev 209-212 Back

51   Ev 209-210 Back

52   Ev 209  Back

53   Ibid.  Back

54   On 1 May 2004 the following countries joined the EU: Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia.  Back

55   Ev 212 Back

56   Ev 210 Back

57   Ev 212 Back

58   Ev 209  Back

59   Ev 201 Back

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