Are you qualified to the 16th Edition IEE Regs? If so I would say you are as qualified as you need to be.
As far as I am aware, when working on either existing or new wiring, you need to be qualified. You shouldn't even work on your own existing house wiring without being qualified.
If you look in the jobs ads in newspapers for electricians you will find they often ask for people to be qualified to the 16th Edition IEE Regs. Unless you wanted to specialise, I wouldn't say you needed anything else.
Best thing to do is to phone an electrical installation company and ask them for advice.