All parties to the contract can do their bit to help improve safety. But ultimately what happens on site is the contractor's responsibility.
Safety is best served by recognising this and ensuring that this is understood and respected by all concerned.
Measures which seek to pass part or all of this responsibility on to others, no matter how well intended, will only confuse matters and, as anyone who has ever worked on a building site will tell you, the most dangerous thing of all is confusion over responsibility.
A N Beal (M), 10 King George Avenue, Chapel Allerton, Leeds, LS7 4LH