SW,
The only way that you would not own copyright in any pictures you take is if somebody paid you to take them for them.
The problem you might be running in to is the assumption that any pictures of RAF aircraft must have been taken either by an RAF/MOD photographer or by another professional. Frankly, I would consider it a bit of a cheek to hear such a suggestion; unless a picture has CROWN COPYRIGHT stamped all over the back, why the hell should someone assume I didn't take it myself?
But, should you run into someone being awkward, I would suggest something along the lines of:
"I confirm that I took this photograph on [DATE], that I am first author of it within the meaning of Section 9(1) of the Copyright, Designs and Patents Act 1988, and that I have not assigned my copyright in whole or part to any other person."