I was told at least a year ago that "new" building regulations in the UK meant that for Building Control to "sign off" a project, a completion certificate was mandatory, and have since used this as a selling point.
I am now told by a building that he checked up on this, found out it was untrue, and feels cheated that I used this.
If indeed I am wrong, I will need to make an offering to him - I really don't want to loose any clients :-)
I'm not aware of any official requirement for a final certificate at this time, although I'm not involved with new buildings. The contractor/developer may require one as part of the contract, of course.
There are plans afoot to include electrical work in the building regs. Have a look here for a discussion we had about this a couple of months ago. The thread contains a link to a long PDF government proposal document.
Steve, Building Regs in England & Wales may not yet require you to provide an Electrical Installation Certificate, but for your work to comply with BS 7671 a certificate should be issued. If you want to join the NICEIC or ECA/SELECT you are required to certify your work and keep copies for your records. Keep up the good work, it sets you apart from the cowboys.