Parliamentary Boundary Reviews: What Next? Contents


1.There are currently 650 parliamentary constituencies in the United Kingdom, each electing one Member of Parliament. There are four Independent Boundary Commissions (the Commissions), one for each constituent nation of the UK, which develop proposals for constituency boundaries in accordance with rules set out in legislation.1 Parliament then decides whether to implement the Commissions’ recommendations. If they do, the new boundaries come into force at the next General Election.

2.Constituency boundaries, and the process of drawing them, are therefore a vital underpinning to the UK’s democracy. They can influence the number of seats parties win in an election and who is elected as an MP to represent a particular community. The Commissions are required by law to propose a new set of boundaries by 1 October 2018 (the 2018 Review).2 These new boundaries would implement the reduction in the number of MPs to 600 and the new rules for boundary reviews introduced in 2011. However, since the 2017 General Election there has been repeated speculation that the Government may not be able to secure a majority in the House of Commons to implement them.3

3.On 9 January 2018, we took oral evidence from the four Boundary Commissions; and Professor Jane Green of the University of Manchester, Professor Ron Johnston of the University of Bristol and Professor Roger Scully of the University of Cardiff; to explore the implications of not implementing the 2018 review. The Boundary Commissions provided further evidence in writing after the evidence session. We thank all of those who gave evidence to us.

4.Given the uncertainty over whether Parliament will support the implementation of the 2018 review, this report addresses the question of whether it would be practical to hold a new review that could be implemented prior to a general election in May 2022. This would require primary legislation. The report also highlights the potential costs and risks of amendments to the current timetable for carrying out boundary reviews that would be necessary to deliver new boundaries by 2022, and the problems with continuing to use the existing, arguably out of date, boundaries.

5.It concludes that it may be possible to cancel the current review and begin a new one that could be implemented in time for an election in 2022, but only if the Government takes immediate action, rather than wait until the autumn to make a decision.

The Boundary Commissions

6.The UK’s system for drawing boundaries is explicitly non-partisan, with a high-level of openness and significant opportunities for public consultation.4 Proposing new parliamentary boundaries is the responsibility of the four independent Boundary Commissions which cover England, Wales, Scotland and Northern Ireland respectively. The Deputy Chair of each commission is a High Court Judge (or Judge of the Court of Session in Scotland) from the relevant judiciary, supported by two other independent commissioners.5 Assistant commissioners can also be appointed to assist in carrying out reviews. The Commissions have a permanent secretariat, headed by the Secretary to the Commission.

7.Each Commission makes its final recommendations to the Government which then implements all four reviews, without being able to amend them, via a single Order in Council approved by both Houses of Parliament.6 The new boundaries come into force for the next General Election.

Development of the Boundary Review Process

8.The principle of all Parliamentary constituencies being represented by a single member, drawn by independent standing Boundary Commissions using a single set of rules, and periodically reviewed, was established through a series of reforms during the 1940s.7 Previously constituencies had been defined in statute. The House of Commons (Redistribution of Seats) Act 1949 set the framework for the rules for redistribution that were broadly in place until 2011, albeit with repeated amendments.8 They were:

9.No rule had supremacy, and following the House of Commons (Redistribution of Seats) Act 1958 (see paragraph 11 of this report) the Commissions prioritised respecting existing constituencies and local government boundaries where they could, making maintaining numerical parity in electorates harder. Owing to the fixed floors on their allocation of seats Scottish and Welsh constituencies were smaller than English ones. The setting of the electoral quota based on the number of seats recommended in the previous review led to an upwards trend in the number of MPs, as any new seats that were recommended in one review then became part of the baseline for the next.10

10.Between 1949 and 2011 there were several amendments to the rules. In 1958 the period between reviews was increased to 10 to 15 years, from the previous 3 to 7 years, and then reduced back to 8 to 12 in 1992.11 The, then Labour, Government decided not to implement the second periodic review which reported in 1969.12 The Conservatives alleged that this was owing to the bias in the old boundaries to Labour, and the Conservative Government of Edward Heath implemented the review in full in 1970.13

11.Most significantly, in 1958 reforms were introduced with the intent, according to the then Home Secretary R. A. Butler, “to bring in a presumption against making changes unless there is very strong case for them”.14 This was in part a response to the previous redistribution where it was perceived that there had been too many changes to constituencies to maintain electoral parity. The 1958 Act shaped the Commissions’ approach to subsequent reviews.

‘Bias’ in Boundaries

12.Overall the rules and the way the Commissions interpreted them led to substantial differences in constituency electorates. Excluding island seats, in 2010 when the last review was implemented constituencies ranged from 40,707 electors in Arfon to 91,531 in East Ham.15 These differences are not randomly distributed. At the 2015 General Election seats won by the Labour Party had on average approximately 4,000 fewer registered voters than those won by the Conservatives.16 This reflects the geographic distribution of the parties’ voters, the systematically smaller constituencies in Scotland and particularly Wales, and the higher propensity of groups that tend to be more likely to vote Conservative to register to vote, rather than any deliberate bias in the system.17

13.It has been estimated that at the 2001 General Election, fought using the boundaries introduced in 1997, if the Labour and Conservative parties had received the same vote share, Labour would have received 142 more seats.18 The Conservative Party subsequently included proposals to change the rules for redistribution to put much greater emphasis on electoral equality in their manifesto for the 2010 General Election.19

14.However the ‘bias’ in the system has not remained fixed. The new boundaries introduced in 2010 did not equalise constituency sizes, with only 39% of constituencies having electorates within 5% of the average UK seat.20 But at the 2015 General Election the Conservative party was favoured by 58 seats,21 and by 11 seats at the 2017 General Election.22 This is because ‘bias’ in boundaries is only partly a result of differences in constituency size. The relative propensity of a party’s supporters to vote, the effective targeting of campaigning resources to marginal seats, a ‘third’ party disproportionately taking votes or seats from one party, or the geographical distribution of a party’s support can also boost the number of seats a party receives for the same number of votes.23

15.Hence the swing in apparent bias in the system from the Labour Party to the Conservative Party between 2001 and 2015 was only partly a result of the new boundaries introduced in 2010 (2005 in Scotland). It also reflected the fact that the Conservative party won 27 seats from the Liberal Democrats, whilst the Scottish National Party, with its geographically concentrated vote, took 40 seats from the Labour Party.24

16.Any set of rules for drawing boundaries leaves a significant number of options for any single local area.25 Which option is eventually chosen can have a significant effect on a party’s prospects of winning an individual seat.26 The political parties therefore seek to influence reviews to their advantage during the public consultation on local proposals.27

17. During the English review between 2000 and 2007, one or more local political parties felt it worthwhile to trigger local inquiries in 66 of 82 local areas to contest the proposed boundaries.28 The investment of the national Labour Party in organising their submissions to the previous review during the 1990s was later perceived by commentators as potentially being worth between 12 and 20 extra seats to the party, which increased the apparent bias in the boundaries during the 2000s.29 The other parties increased their engagement in the subsequent boundary review.30

Coalition Government’s Reforms in 2011

18.The Parliamentary Voting System and Constituencies Act 2011 (the 2011 Act) reformed the rules for redistribution.31 As well as reducing the number of MPs in-order to “reduce the cost of politics”, the reforms were intended by the Conservative Party to address what they saw as biases in the existing system that favoured the Labour Party.32

The new rules: 33

19.Standardising the electoral quota across the UK, so seats are distributed between the constituent nations of the UK differently, combined with the reduction in the absolute number of seats, results in all four nations having a reduced number of MPs. The table below sets out the changes from the current distribution compared to the 2018 review.


Old Seats

New Seats














Northern Ireland








20.The 2011 Act also made amendments to the process of public consultation. The previous requirement for formal public inquiries into any proposals that were subject to objections by a local authority or a group of 100 residents was removed.35 Instead, the Commissions were required to hold between two and five public hearings in each of Scotland, Wales Northern Ireland and the nine English Regions, to last for no more than two days each. Oral representations could be made, but not questioned or contested by other interested parties as in the old inquiries.36

21.The first review under the new rules was fixed in the Act to report in October 2013, eighteen months before the 2015 General Election. Given the provisions of the Fixed Term Parliaments Act it was assumed that each five-yearly review would continue to report 18 months prior to the next General Election. There is no provision to amend the dates of reviews in the event of an early election. The requirement to report in 2013 was subsequently changed to 2018 by the Electoral Registration and Administration Act 2013, after the Liberal Democrats withdrew their support for the 2013 Review when reform of the House of Lords did not achieve a majority in the House of Commons. This ended the 2013 Review.

Uncertainty about the 2018 Review

22.The 2018 Review was launched in February 2016, in line with provisions of the 2011 Act. Following the 2017 General Election, given the likely opposition of opposition parties to the implementation of a review under the 2011 Act,37 there has been ongoing speculation as to whether the 2018 Review will be cancelled.

23. There has been media speculation that the Democratic Unionist Party (DUP) will not support the final recommendations of the Boundary Commission for Northern Ireland (BCNI).38 Under the 2011 Act all four Commissions’ recommendations must be put to Parliament by the Government simultaneously and without amendment.39 If the BCNI’s initial proposals, which reflect a reduction in the total number of Northern Irish seats from 18 to 17, had been used for the 2017 General Election the DUP would have won three fewer seats and Sinn Fein two more.40 In their response, the DUP stated their opposition to the principles underlying the reforms in the 2011 Act, as well as the detail of the proposed boundaries.41 The BCNI released their revised proposals for consultation on 30 January.42

24.Notwithstanding the final position the DUP takes, several Government backbenchers have suggested that the decision to leave the European Union calls into question the desirability of reducing the number of MPs owing to the responsibilities that are now due to be repatriated to the UK Parliament.43 Some Members have also raised questions about the impact of specific proposals on their local areas.44

25.Given these uncertainties the Government cannot be confident at this time that there will be support in the House of Commons to implement the recommendations of the 2018 Review. Therefore, unless a decision to cancel the review is made in the interim, the uncertainty and speculation concerning the 2018 review will continue until the autumn.

1 Parliamentary Constituencies Act 1986, schedule 2 (as amended)

2 Parliamentary Constituencies Act 1986 (as amended by Electoral Registration and Administration Act 2013, Section 6).

4 ACE Electoral Knowledge Network ACE Encyclopaedia: Boundary Delimitation 2nd Ed (2013) accessed 28 December 2017

5 The Speaker of the House of Commons is the Chair ex officio of each commission, but takes no active role in their work.

6 Prior to the Parliamentary Voting System and Constituencies Act 2011 recommendations from individual commissions could be implemented separately.

7 For a summary of the history of redistribution see, Neil Johnston “The Parliamentary Constituencies (Amendment) Bill 2017–19 Briefing Paper CBP 08146, House of Commons Library, 1 December 2017 pp12-16.

8 They were consolidated with later amendments into the Parliamentary Constituencies Act 1986, which, as amended, remains the substantive statute.

9 N. Johnston, “The Parliamentary Constituencies (Amendment) Bill 2017–19”

10 ibid

11 Oonagh Gay & Isobel White “Parliamentary Voting System and Constituencies Bill 2010”, Research Paper 10/55, House of Commons Library, 01 September 2010

12 ibid p30

13 ibid

14 Quoted in ibid p29, this became the House of Commons (Redistribution of Seats) Act 1958.

15 Political and Constitutional Reform Committee, Eighth Report of Session 2014–15 What next on the redrawing of parliamentary constituency boundaries? HC 600, para 25. The constituencies protected in the 2011 Act were the existing Na h-Eileanan, and Orkney and Shetland constituencies and two on the Isle of White (which is currently covered by one large constituency).

16 John Curtice, “The Geographical Challenge: How Winning Elections Has Become Much More Difficult for Labour”, The Political Quarterly, Vol 88, No. 1, January-March 2017 pp 13-19

17 ibid

18 Labour won 355 seats with 35.2% of the vote and the Conservatives 198 with 32.4%. The calculation assumes both parties received 33.8% of the vote and applies a universal national swing. It does not take into account how the behaviour of third party voters or the parties’ decisions on where to target resources would have been effected, so is only a guide. Ron Johnston, Charles Pattie and David Rossiter, “Local Inquiries or Public Hearings: Changes in Public Consultation over the Redistribution of UK Parliamentary Constituency BoundariesPublic Administration, Vol 91, No. 3, (2013) pp 663-679.

19 Ron Johnston, David Rossiter & Charles Pattie, “When is a Gerrymander not a Gerrymander: Who Benefits and Who Loses from the Changed Rules for Defining Parliamentary Constituencies?” The Political Quarterly Vol. 88 No. 2 (2017), pp 211-220

21 Johnston et al “When is a Gerrymander not a Gerrymander”

22 Q72

23 Johnston et al “When is a Gerrymander not a Gerrymander”

24 Labour won 12 Liberal Democrat seats. In 2015 the SNP won 56 seats with 4.7% of the UK wide vote, compared to the one seat the UK Independence Party won with 12.1% of the vote; General Election 2015, Briefing Paper CBP7186, House of Commons Library, 28 July 2015. Curtice, “The Geographical Challenge”; Q70 & Q74.

25 Q47

26 “The Electoral Reform Society “Fair Boundaries”, accessed 31 January 2018

27 Q64

28 Johnston et al “Local Inquiries or Public Hearings?”

29 ibid

30 ibid

32Government publishes AV referendum Bill”, HM Government, 22 July 2010.

33 The rules are contained in Parliamentary Constituencies Act 1986, Schedule 2 (as amended by the 2011 Act).

34 Parliamentary Constituencies Act 1986, Schedule 2, 5 (1)

35 Johnston et al “Local Inquiries or Public Hearings?”

36 ibid

38 See for example, “Boundary review plans abandoned as DUP will not back proposals” Daily Express, 18 June 2017, “Nigel Dodds: Boundary Commission’s constituency proposals need radical change” (Belfast) Newsletter 18 October 2017

39 Q14

40 Martin Baxter, “Northern Ireland: New Constituency Boundaries 2018” on accessed 20 December 2017

42 “Boundary Commission for Northern Ireland “Revised Proposals consultation”, 30 January 2018

43 HC Deb, 01 December 2017, Col 611

44 See for example Q33-37 or HC Deb, 01 December 2017, Col 590 & 591

16 February 2018