Do I need permission to lay new drains and/or install a septic tank within the boundary of my property?

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.

Except in an emergency, your local authority should be given at least 24 hours notice of any intention to repair any underground drain (section 61 of the Building Act 1984).