Why should your pension be affected.
Your original contract with the RAF required you to serve X number of years and then you would be entitled to a pension, deferred of otherwise. Should you come back BECAUSE THEY WANT YOU, then they should pay you the rate for the job and leave your pension alone. It's a different contract!
I worked for civilian helicopter company and on my retirement they were strapped for pilots so I continued as a contract pilot. A different pay arrangement because they did not have to pay my pension or NI contributions. There was no question of my company pension being affected. I had the option of chucking it in if I felt like it but they had the option of showing me the door if they didn't want me.
I did this, on and off, for eight years.