It's probably about right for a cheapo CU, basic testing and an assumption that nothing will go wrong.
bhm - ask him what make/model of CU he will be installing, how many sections it has, will there be any RCBOs, how many spare ways you'll be left with, whether he will test your installation before he installs it or only afterwards, and does his £250 include sorting out any problems that the new board uncovers, such as N-E faults and borrowed neutrals.
As ever, personal recommendation is always the best way to find a reputable tradesman, but if you're having to go ahead without much in the way of references or personal recommendation, don't put any store by registration itself - sadly it is possible to become registered with woefully inadequate qualifications and zero practical experience. You don't have to spend long here to see people cropping up who are registered and "qualified", but who are clearly seriously incompetent in reality and who should not be charging for their services.
Did you know, for example, that this electrician could be legitimately trading and yet never have changed a CU before? You could be his guinea pig.
It's your money and you have every right to ask prospective tradesmen what their qualifications are.
Just being listed here is not a good enough guide. No genuinely experienced electrician, with the "full set" of C&G qualifications will mind you asking - in fact he will wish that everyone was like you.
I feel sorry for people who have been misled by training organisations and (shamefully) the Competent Person scheme organisers into thinking that a 5-day training course, a couple of trivial examples of their work and some basic understanding of how to use test equipment will make them an electrician, but not sorry enough to agree with them trying to sell their services to Joe Public.
