Be aware that CAP804 is advisory only and there is no current plan to release an updated copy. Sadly it is also the only place that contains any information pertaining to military accreditation......
Its down to the Head of Training of your chosen school to assess your experience and put together an appropriate programme. You will have to do all the exams and flight training and this will involve you going through the CPL/IR as you can't direct access an ATPL unless taking a skill test on a multi pilot aircraft which grants you only that type rating. Your military instrument does count towards the training but you cant keep it current on the basis of a military IRT which means a yearly test with a CAA examiner or renewal on leaving the mob but ensuring you don't hit the 7 year barrier.