Never heard of anyone going RAF to Army though
Well, I can think of 2 - G***** Sh***** and A* H*****. Former was last seen by yrs truly as a Sqn Cdr in BAOR while the latter - an ex-SH-crewman - went on to have a successful flying career as Driver Airframes. Got himself commissioned too.
Mind you, these were both late 70s/early 80s...