Why a British emergency escort would start with River class

What hull would Britain use for a modern war-emergency escort?

A River-class hull, probably enhanced for the emergency role, would be the most practical starting point.

Accelerating existing Type 26 or Type 31 orders differs from creating a true war-emergency escort. For rapid construction, a River-class hull or an enhanced version of it would be the starting point. The design's availability makes it a more practical emergency foundation than trying to compress the schedules of larger, more complex combatants.