Once you are out of the RAFVR, there is little chance that you would be called up ahead of anyone else - unless per chance you were a highly skilled operator of an ex-militray type. That aside could you really see the production rate of aircraft in an all-out war losing that many pilots to require conscription, to be able to be ramped up with today's modern hi-tech fighters? Not a chance - we would have been invaded before that could even happen.
Although it is possible to convince an interviewer of your interest, have you considered the possiblility that you may be that enthusiastic about it once in, that you join anyway? It has happened to plenty, hence its fantastic use as a recruitment tool.
Glad your interest was sparked by that post!
And what exactly is the downside to being called up as a fast jet aviator?