From personal experience on the UK airshow circuit I wouldn't go there - even big shows like RIAT only turn a relatively modest 'profit' on an average year (their latest accounts are on-line). Things like public liability insurance can be difficult and expensive to get and of course you are at the complete mercy of the British weather as someone has already pointed out. There's also the problem of finding an appropriate slot in the calender when the other big shows aren't taking place and drawing away your prospective audience (as the organisers at the RAFA Shoreham show will testify).
That said, if your intent on trying to run something you may want to have a chat with the guys at Kemble Air Services who run the various Kemble air shows - they'll give you a heads-up on what's involved.