Great advice everyone, thanks. Didn't know about the 'multi-crew' rating thing; the relevant bits on the ratings page of my license are 'ME Piston (Land)' and 'IR-SPA-ME', I did my test on a Beech Duchess so was assuming that I'd be OK to hire something similar and fly it by myself - is this assumption true?
I'm starting to wonder whether getting an AOC might be the way ahead but am daunted by the prospect - is it too much for an individual to achieve do you think? Also I guess it will cost a fortune. Will the CAA want to know which aeroplane I am going to fly (i.e. the reg no), and who maintains it etc, or can you get an AOC to operate without specifying which aircraft you will be using?
Guess I'll have to call them soon, but it's as well to know as many of the facts first, or else I imagine it will be easy to be dismissed by someone who is too busy to speak to an unprepared muppet