Well, to the 9 battleships and battlecruisers of the Royal Navy sep -39 in the Atlantic, there were also 4 at Alexandria for combined number of 13. Barham, Royal Oak, Hood and Repulse were sunk, but the following were added:
HMS Valiant feb -40 (refitting)
HMS King George V dec -40
(HMS Prince of Wales may -41, sunk at Singapore)
HMS Duke of York dec -41
HMS Queen Elizabeth march -41 (refitting)
So in spring -41 RN had: 4 BBs Queen Elizabeth class, 4 BBs Royal Sovereign class, 2 BBs Nelson class and 2 BBs KGV class, as well as 2 battlecruisers.
(In dec -41, two BBs at Alexandria were immobilized by Italian frogmen)
In spring -42: 2 BBs Queen Elizabeth class, 4 BBs Royal Sovereign class, 2 BBs Nelson class and 2 BBs KGV class, as well as 1 battlecruiser.
Even if you rate those of WWI classes (Queen Elizabeth, Royal Sovereign, Nelson) at 0.75 or something like that, you wouldn’t arrive at 4-6 battleships for one A&A BB. You could argue that UK should have 2 BBs at-start, but that could be a bit too much for play-balance. In AA50, cruisers might represent not just heavy cruisers but also smaller concentrations of battleships, and this would make it logical for UK to have more than one cruiser at-start.