When I came to the UK several years ago I had a UK passport(Father) and a NZ passport (Birth). I wasn't permitted to join as a Brit because of lack of residency, so I joined under the jolly commonwealth scheme. However, back in the mid-nineties it seemed to be the luck of the draw.
An Ozzie mate (yeah, some of them are alright) also tried to join the RAF under the Commonwealth entrant scheme (he had an Australian passport and also a Brit one from his father who had been a Gp Capt in the RAF) but was told there was no such thing. Without residency, this didn't leave him many options. So he asked the same of the RN who, after putting him through the usual selection blah, offered him a place as a Navy Pilot under the Commonwealth scheme. He then took the acceptance letter to the RAF recruiting office who still blatantly refused to accept the existance of such a scheme. Not wanting to rock the boat (no pun intended) he took the Navy up on the offer and flew with the fishheads.