Mass-produced 12-inch British battlecruisers

What if Britain mass-produced cheap 30-knot battlecruisers with 12-inch guns after Japan left the treaty system?

If built with spare capacity rather than replacing battleships, they could equip Commonwealth navies and multiply fast forces in the Atlantic, Mediterranean, and at Denmark Strait.

Building these ships instead of full capital ships would leave Britain short of heavy units, but using otherwise spare capacity changes the calculation. Several could become flagships for Canadian, Australian, or Indian forces and reinforce fast groups such as Force H. Six or more 12-inch ships would provide useful speed and enough firepower to complicate encounters with Deutschlands, Dunkerques, and Bismarck.