At the start of the construction phase of the project, the responsibility for Health and Safety is transferred from the Planning Supervisor to the Principal Contractor. This is normally as soon as the Principal Contractor is appointed.

Before construction can begin, he is obliged to develop the pre-contract Health and Safety Plan, and obtain the agreement of the Client that the health and safety issues have been adequately addressed in the Plan. He is then obliged to maintain the Plan throughout the construction phase. There are obligations to provide information to those affected.

The responsibility for co-ordinating all the various contractors and trades present on any construction site rests with the Principal Contractor, and there are obligations on all concerned to co-operate. Everyone visiting the site, even the Client, is obliged to follow the Principal Contractor's directions on Health and Safety

On completion of construction, the responsibility for the site reverts to the Client. The Principal Contractor hands over information from the Health and Safety Plan, required for the Health and Safety File, to the Planning Supervisor.