Why Britain did not build a larger Vanguard class

How many Vanguard-class battleships could Britain have built?

Potentially several, but only by diverting shipyard effort from carriers, and the Royal Navy no longer needed that many new battleships.

Another hull could physically be built, but yards, skilled labour, machinery, and weapons had to be divided between battleships and the carrier force. More Vanguards were possible if Britain prioritised them. Carriers offered greater value in the strategic environment at the end of the war, which closes the dreadnought story on a question of opportunity cost.