How Type 42 kept Royal Navy destroyers small

Why did Royal Navy destroyers remain small for so long after the cancellation of CVA-01?

The cheaper Type 42, originally meant to complement Type 82, was treated as a substitute for it, and the planned number of ships was then cut too.

The Type 42 was conceived as a lower-cost Sea Dart destroyer that would complement Type 82 in the planned CVA-01 force. Once officials compared two ships carrying the same destroyer label, the cheaper Type 42 displaced the larger design; procurement then reduced the number bought as well, producing savings in both ship size and hull count.