What determines the Lion class's successor battery

Would a successor to six Lion-class battleships carry twelve 16-inch guns or nine 18-inch guns?

Twelve 16-inch guns in peacetime without Yamato intelligence, but nine 18-inch guns if Britain knew the threat and expected war soon.

After six Lion-class ships, Britain would need to choose between a larger salvo and a larger shell. In peacetime without firm intelligence on Yamato, twelve 16-inch guns offer a logical development of the existing programme. Knowledge of Japanese 18-inch weapons changes the competitive requirement. If war also appears close, nine 18-inch guns become the more plausible answer despite the greater design disruption.