Posted By Ken Taylor My understanding is that if the Principal Contractor has control of the site both the 1957 and the 1984 Acts will apply. By way of hypothesis, if the 1984 Act did not apply, the Common Law duty of care to trespassers (as prior to the 1984 Act) would. Irrespective of the above, Section 3 of the Health & Safety at Work, Etc Act will be applicable.

Posted By Adrian Watson If a contractor is in occupation of the site for the purposes of the Occupiers Liability Act 1957 he will owe lawful visitors a duty to see that the premises are safe for the purpose of their visit. A contractor who does not control the works is not in occupation of them. During the execution of the works, an employer who retains control of the premises will be liable as an occupier to third parties. Where damage is caused to a visitor by a danger arising from faulty execution of any work of construction, maintenance or repair, the employer will have a defence if he acted reasonably in entrusting the work to an independent contractor and took steps to satisfy himself that the contractor was competent and that the work had been properly done. Where the occupier is or should be aware that a trespasser may at risk from a danger on the site and it is a risk against which, in all the circumstances, the occupier should offer protection, he owes the trespasser a duty to see that he does not suffer death or personal injury by reason of that danger. See Halsbury's Laws of England 4th Edn Para 459 et seq