If I want to lay new drains and/or install a septic tank, within the boundary of my property, will the building regulations apply?

Department: Environment Services
Division: Environment Services/Building Control

YES - they will apply to new rainwater or foul drains inside, as well as outside the building.

The building regulations also apply to all non-mains foul sewerage arrangements (i.e. those using septic tanks), including their outlets and drainage fields. If the work involves a drain which is less than 750mm below the surface of the ground, and you employ an installer registered with the Institute of Plumbing, you will not need to involve the building control department. For further details of the Institute of Plumbing please contact 01708 472791.