Hi Modelman,
Most of the information is in this AIC
http://www.nats-uk.ead-it.com/aip/cu...8_W_070_en.pdf
It looks as if you are ok as long as you are operating from a licensed airfield and the charity is registered. Just check Annex 1 of the above document, which lists aircraft and pilot requirements.
Events like Starlight Day at Popham and Burned Children’s Club Day at Bourn seem to attract a variety of aircraft out with the above specification, but in those cases there is no financial element.
Safe Flying,
Richard W.
Edited to say Whopity looks to be on the same lines