With a fair bit of restaurant cooking experience, I can assure you that people will be prepared to pay almost ANYHTING if you manage to give them an unforgettable evening for that!
If they have enjoyed the evening they'll recommend you... but if you go for a moderate price and they will immediately sense that compromises to keep that low price have been made. Don't be average - get an excellent cook (sorry, I don't live in the UK

) and keep a strict guest limit - I'd say no more than 15 people. You don't necessarily need a kitchen, if your cook is a skilled one he'll know how to his prep off-site and do only the final arrangements at the dinner location.
Small but exclusive - and it'll be a self-runner. Exclusive doesn't mean that it has to be ridiculously expensive, but calculate realistic prices (about 100 - 130 British pounds sounds about right). Invite press people for a free demo dinner, place advertisements including a raffle where people can win a ticket by answering a magic-related question (that way you'll get addresses of potential customers for later advertisements).
Rehearse the evening with all the magicians and serving staff like a theater play, cause that's what it is going to be. Let your guests know when the next magic act in the row is coming (e.g. with quiet music or changing lighting), dont' rip them out of their conversations unexpectedly.
Make it a monthly (quarterly, yearly, ...) event and give it a name. Try to get someone famous as one of your first guests.
German star cook Eckard Witzigmann is doing something similar in a circus-like setting, and he's charging WAY MORE than what we've been discussing on the forum so far.
I'd so much like to be part of that (mostly keen for the cooking part) - wanna fly me in from Scandinavia?
-Magnus