OK, take a look at these figures from 2004:
British Army officers and other ranks, Analysis by rank and sex, at 1st April 2004
Royal Navy and Royal Marine officers and other ranks, analysis by rank and sex, at 1st April 2004
Royal Air Force officers and other ranks, Analysis by rank and sex, at 1st April 2004
354 Captains & above in the Navy (out of 41,000).
748 Colonel & above in the Army (out of 113,000).
459 Gp Capts & above in the RAF (out of 53,000).
So about in propotion (roughly!) in 2004.
In 2008 the requirement for the RAF was 350 but the actual number was 440!
See
House of Commons Hansard Written Answers for 02 Jun 2008 (pt 0033)
I can't find the 2009 figures but I guess this is why there has been a paucity in Flt Lt to Sqn Ldr promotions recently (about 60 on the recent flying-branch list vice about 120 in recent years!
); I guess they're doing something about it now?
The B Word