The Air Navigation Order in CAP393 (pages 202/3 of 480) appears to be pertinent.
http://www.caa.co.uk/docs/33/CAP393.pdf
Part 34 Public Transport and Aerial Work
Articles 267: exceptions - cost sharing and
268: exceptions - recovery of direct costs make specific references to
direct costs
Article 265: exceptions - flying displays makes specific reference to the recovery of "direct costs of the flight
and a contribution to the annual costs of the aircraft"
So by implication as the highlighted words in A265 do not appear in Articles 267 or 268, annual costs are not part of costs that can be shared on a private flight.
But like so much legalese, perhaps still open to interpretation.