Likewise in the present case I think that it was part of the conduct of Octel's undertaking at Ellesmere Port to have the chlorine tank repaired. But I would not accept the extreme position of Mr. Carlisle Q.C. for the Crown, who submitted that "works of cleaning, repair and maintenance which are necessary for the conduct of the employer's business" attract the duty under section 3(1). That would suggest that any repairs, cleaning or maintenance, wherever and by whomsoever they may be done, form part of the conduct by the employer of his undertaking. The cleaning of the office curtains at the dry cleaners; the repair of the sales manager's car in the garage, maintenance work on machinery returned to the manufacturer's factory: all would in principle impose upon the employer a duty under section 3(1) to ensure that they did not create risks to the health and safety of workers and others at the drycleaners, garage and factory respectively. Mr. Carlisle said that the employer could always rely on the defence that it was not reasonably practicable to take steps to prevent risks arising from what other people did on their own premises. But I do not think that such a defence needs to be invoked. In the context of the Act, such activities cannot fairly be described as the conduct by the employer of his undertaking. If he has a repair shop as a part of his plant, that is an ancillary part of his undertaking. Likewise, as in this case, if he has independent contractors to do cleaning or repairs on his own premises, as an activity integrated with the general conduct of his business. But not in the case of activities carried on by another person entirely separately from his own.

It seems to me wrong to try to find some formula such as that of Mr. Carlisle to take the place of the simple words of the statute. Whether the activity which has caused the risk amounts to part of the conduct by the employer of his undertaking must in each case be a question of fact. The place where the activity takes place will in the normal case be very important; possibly decisive. But one cannot lay down rigid rules. A difficult borderline case was RMC Roadstone Products Ltd. v. Jester [1994] 4 All E.R. 1037. The employers engaged contractors to repair a building. The employers were going to buy new asbestos sheets for the purpose but the contractors offered to remove some from an adjacent disused factory. The employers obtained the permission of the owner. Their projects manager inspected the site with the contractors and warned them to be careful. They offered to supply the contractors with equipment. One of the contractors fell through a skylight on the roof of the disused building and was killed. The employers were charged under section 3(1) and the justices convicted. They said that it was not necessary for the employers to control the site on which the work was done. They were in a position to give specific instructions to the contractors as to how it should be carried on. They therefore owed a duty under section 3(1)

The Divisional Court set aside the conviction. Smith J. said, at p. 1047:

  "I am unable to accept that the mere capacity or opportunity to exercise control over an activity is enough to bring that activity within the ambit of the employer's conduct of his undertaking. Before he can say that an activity is within his conduct of his undertaking, the employer must, in my judgment, either exercise some actual control over it or be under a duty to do so. If the principal chooses to leave the independent contractor to do the work in the way he thinks fit, I consider that the work is not within the ambit of the principal's conduct of his undertaking. It is wholly the contractor's undertaking."

I am afraid that I cannot accept this reasoning, which seems to me to involve a circularity. The employer is under a duty under section 3(1) to exercise control over an activity if it forms part of the conduct of his undertaking. The existence of such a duty cannot therefore be the test for deciding whether the activity is part of the undertaking or not. Likewise, the question of whether an employer may leave an independent contractor to do the work as he thinks fit depends upon whether having the work done forms part of the employer's conduct of his undertaking. If it does, he owes a duty under section 3(1) to ensure that it is done without risk--subject, of course, to reasonable practicability, which may limit the extent to which the employer can supervise the activities of a specialist independent contractor. Although the case was very much on the borderline, I think that there was evidence upon which the justices were entitled to find in the particular circumstances of the case that having the asbestos sheets removed was part of the employers' undertaking. The facts were a matter for them and their decision should not have been disturbed.

As the question of whether having the tank repaired was part of the conduct of Octel's undertaking was also one of fact, it should properly have been left to the jury. Even if, as I think, the only rational answer was yes, it should still have been left to the jury: Director of Public Prosecutions v. Stonehouse [1978] A.C. 55. The judge did not do so. The effect of the summing up was to direct the jury to find on this point for the prosecution. This was understandable because the case was conducted on the basis that the sole issue was whether the fact that RGP were independent contractors took the work outside the scope of Octel's undertaking. Having correctly ruled that it did not, the judge assumed that the matter was no longer in issue. But in my view there remained a question of fact which it was strictly speaking for the jury to decide.

The question then is whether this House should as in Director of Public Prosecutions v. Stonehouse apply the proviso to section 2(1) of the Criminal Appeal Act 1968 and dismiss the appeal. The test for whether the proviso may be applied was laid down by this House in Stirland v. Director of Public Prosecutions [1944] A.C. 315, 321. The House must be satisfied that "a reasonable jury, after being properly directed, would, on the evidence properly admissible, without doubt convict." In written submissions after the argument in the House, the appellants submitted that this test was not satisfied. They said that they elected to call no evidence after the judge had wrongly ruled in favour of the Crown's submission on the law. If the judge had construed the statute correctly, they would have been able to adduce evidence to show that they had no control over how the tank was repaired and that it was therefore not part of their undertaking.

If the appellants were right about the law, I think that there would be much force in this submission. But if, as I think, the question of fact which should have been left the jury is simply whether having the tank repaired was part of the conduct of Octel's chemical undertaking at Ellesmere Port, I cannot imagine what evidence could have been called by the appellants which would have led a properly instructed jury to return a negative answer. The tank was part of Octel's plant. The work formed part of a maintenance programme planned by Octel. The men who did the work, although employed by an independent contractor, were almost permanently integrated into Octel's larger operations. They worked under the permit to work system. Octel provided their safety equipment and lighting. None of these facts was disputed. In these circumstances, a properly instructed jury would undoubtedly have convicted. I would therefore apply the proviso, dismiss the appeal and affirm the conviction.