The job should involve a full test and inspect afterwards as all circuits lead to the board. It is not a 'minor works'. You are looking for an NICEIC sparky really, although there are other registration boards now. That certificate will be important though if you get any problems, so make sure it's there.

A 16th Ed should be ok at this stage. It takes time to bring the new regs in so... I've seen job ads still asking for the 16th Ed :)

Ooh yeah. Maintenance. That's a separate contract. And guarantee's are only compulsory under NICEIC or other registration boards. So be careful there.