Babcock could probably churn out a couple of Type 31 to some spec or another fairly rapidly - or at least, well within the time scale projected. Given Babcock are already making complex hull assemblies for the Virginias.No capacity in any UK yards whatsoever
Their order book for the existing run of Type 31 is about half way through. Unlikely choice if they wanted to run 10 or 20 out the door but if they just need a working couple delivered, even if just ready to be fitted out in the states, could work.
We both know there's zero chance that the design won't be overhauled however