As a principal contractor, when do I have to prepare a construction phase plan for health and safety on the site?

You need to prepare the plan before the start of construction work for all jobs that are notifiable. The plan should be specific to the particular site or project, and set out how you will manage the construction phase and the key health and safety issues for the particular project. Keep the plan relevant – it should be a practical aid to help you. There is more information about this in Appendix 3 of the ACoP L144. Although you don’t need to have a written health and safety plan for non-notifiable projects, you will still need to plan and manage these aspects of the construction phase appropriately.