Only you can answer that!
Once you have been selected for the RAF, tolerated all the uncertainty and bull$hit involved in the current era, passed elementary flying training, initial officer training, basic flying training (if you're lucky, MELIN rubbish if you're not), advanced flying training, operational conversion, squadron acceptance and combat readiness, you will be a Qualified Service Pilot.
If you did a multi-engined OCU for an 'approved' type, then once you've gained 2000 hours total time, of which 1000 must be as P1C on an approved ME type, 500 as P1 under supervision, then you will be exempt from any requirements to obtain an ATPL/IR except:
Pass ATPL Air Law
Have an IRT observed by a CAA Staff Examiner
Fill out the form and pay the dosh.
If you were a FJ mate, you can only obtain a CPL/IR with ATPL knowledge. But you'll need to do a bridging course, pass 5 exams and get an IR on something like a Seneca.
If you were a helicopter pilot - sorry, not much accreditiation available towards an ATPL(A).