Beagle -
If you can show that you have held a military ATC licence then you are exempt from navigation and met exams... otherwise you do the same course.
Civvy ATC is a hell of a lot different from Mil - even basics such as aerodrome control and how we as civvies use strips instead of the old pin boards etc etc.
Mil guys have to learn all about civvy operations, including the ANO etc etc.
It's not like flying multi engine in the forces then transitioning to type rating in a civvy aircraft - flying is flying at the end of the day and if you can do it, you can do it (in fact I would go as far as to say if you can do it in the Mil, then as long as you can stand being civilianised you will have no probs on civvy street performing the task... unlike the otherway around. Most mil flying is far more involved and intense than sitting on an airbus reading the newspaper during cruise and monitoring Ts and Ps).
The controlling is totally different and to go from one to the other in either direction would need the training - how many civvies have to split a four ship arrival and integrate helos etc??
The way that operations are run, say at London TC, would mean that if an ex mil controller was given dispensation to do just the bookwork exams, then train live, it would take a hell of a lot longer for the OJTIs to get him or her to the required standard. Time which I am afraid is not available due to the amount of people that have to be trained, the amount of ATCOs available to do it, the amount of SCT required for other ATCOs etc etc. Although possible theoretically, it is just not feasible.
By the way, before anyone jumps down my throat, I flew in the Mil (badly), decided to increase my lifespan by becoming a mil ATCO, and am now a civvy ATCO, so I know where I am coming from with what I say.
I did the full NATS course and although I would have like to have had it shortened due to previous experience, I am glad it was not in the end. I work at TC and I work a hell of a lot harder more often than I did in the Mil, having been based at some very busy Mil units.
Conversely I know a lot of civvy ATCOs that would struggle at Mil ATC