Chimp Boy
Mymatetcm is correct, if you register to run for public office you get to leave. You could, as someone I know has done recently, PVR and request early dismissal. Alternatively challenge the system and let us all know how you get on.
That used to be the case but I think they closed it in the 60s. Now, IIRC, you actually have to get that public office appointment before you may leave.
Given that you may be an MP and a Reservist there is perhaps no reason why you could not be recalled for reserve service after you got elected
