Why waiting for small-tube boilers carried strategic and industrial costs

Why not delay the Queen Elizabeth programme for a year to give small-tube boilers more time?

An extra year offered no guarantee of suitable boilers and would sacrifice yard time while delaying ships that might be needed for war.

Waiting a year might allow small-tube boilers to mature, but it offered no guarantee that suitable machinery would be available. Idle yards depended on continuing orders and could face commercial failure. Britain would also lose a year of possible construction. Ships held at the design stage would be less likely to enter service before a war, which weighed against waiting for the ideal machinery.