An electrician is calling this evening. Do you have any suggestions on relevant questions to ask or relevant matters to clarify.
Firstly, get a detailed written quote from him and at least two others. By all means tell each of them you are doing so - that way they will be less likely to try to rip you off and may try harder to keep their charges down. Also, it means that if there are problems, you have something in writing.
Secondly, make sure that they are all members of N.I.C.E.I.C., the UK's consumer safety organisation and independent regulatory body for the electrical industry (website listed below). Their website is full of helpful information and you can check to see who your local members are.
Thirdly, you are the customer here: that means you're in charge. Draw up a list of jobs you want done, things you want replaced or added to. If there's something you don't understand, ask (and ask each of the electricians, so you can compare their answers). And then get them to confirm it all, in detail, on paper.
Fourthly, the questions: several people here have come up with good ones. One approach might be to ask your electrician what he will be doing, and then ask the questions. Don't forget to ask how much these extras will cost - it may be that, while you would prefer this switch go there, the cost in time (and hence labour) makes it not worthwhile. If you don't know how much each job will cost, you won't be able to make informed decisions and might regret it afterwards.
So at this point I would go from room to room, making notes as to what you want done in each area, what moved, what added, what taken out (after all, if you're having the whole place rewired, now would be the best opportunity to make all those alterations).
Consider replacing all the single sockets by doubles, and add more sockets in the kitchen (you can never have enough kitchen sockets!).
Are the lights in the right place, and bright enough or too bright? How about dimmers, or extra switches?
Can you reach everything, or are some switches or sockets inaccessible? It might be worth moving them.
Do you have trailing leads or multiple plugs on sockets? Have your friends or family complained about a lack of socket in one corner? If so, add more sockets, closer to the appliances.
Any good handyman or electrician is likely to be busy, so he may not be able to come quickly. Ask him when he will be able to start the job and how long it will take.
Will he make good afterwards (this means replastering where necessary)?
What hours does he work (will he be waking you up in the morning?)?
What will you need to move out of his way beforehand?
Will he provide you with a certificate at the end of it all?
That's about all I can think of.
Good luck!