Just to clear the facts between those with two careers, doctors who then became aircrew and the out of branch aircrew.
The RAF doctors and engineers of 1960s vintage had been commissioned in the Medical and Engineering branches. They may then have serve on operational sqns on out-of-branch tours.
I can't speak with direct knowledge of doctors but on 35 there was an AEO, good egg and all, who at the end of his one tour went back to being an engineer in branch. I think, given his rank and age, that he had probably done a JEngO tour before his training as an AEO. His next tour was OC EES.
Of the former, we had a GD/P co-pilot on Nimrods who was not a doctor but a physiologist (IIRC) who applied to transfer to the Medical branch. The RAF refused, so he joined the RAMC in the rank of major and was returned to medical school to get his medical degree.