I was under the impression that anyone could sit the ATC exams, whether or not they had completed an ATC course - a risky/expensive thing to do but still permissable. There would be no need to leave the 'comfort zone' to obtain the appropriate Licences; this path has been trodden by several to my certain knowledge. Mind you getting the appropriate Endorsements is a different matter!
I understand that Permanent Commissions are rarely awarded in the current unstable climate in MoD recruitment so the option of leaving the 'comfort zone' is no longer a matter of choice.
BTW I agree with your comments, niknak, re. the guys that went the Dundridge route.