Which guns would arm new British monitors?

If Britain built new monitors before the Second World War, what guns would they use?

Reused ships would take spare 15-inch guns; a design with newly manufactured weapons would probably use 14-inch guns.

Two practical armament paths depend on available production. A low-cost monitor could reuse 15-inch guns released by older capital ships, while an all-new mounting would probably adopt the 14-inch caliber then being manufactured for the King George V class. Existing gun stocks and active production lines can outweigh an abstractly ideal caliber.