a)Is this illegal ( I have a PPL with no other qualifications)?
b)Could I be exposed to any claims if any personal injury arises etc?
a) Yes
b) Yes
By auctioning a ticket the flight becomes Public Transport because money has changed hands for the purpose of the flight, Article 157.
Public transport and aerial work - general rules
157 (3) Subject to the provisions of this article and articles 158 to 163, an aircraft in flight shall for the purposes of this Order be deemed to fly for the purposes of public transport:
(a) if valuable consideration is given or promised for the carriage of passengers or cargo in the aircraft on that flight;
It is a trap that many fall into and many clubs will have a Flying Order making members aware of the issue.
There are two ways to conduct such a flight, one is as a "Lesson" which must be conducted by a Flight Instructor and must be advertised as such, the other is in accordance with AIC 70/2008
http://www.nats-uk.ead-it.com/aip/cu...8_W_070_en.pdf but, this requires your charities qualify.