reading recent threads, my rides this week, and the forecasts, suggest that:
Here in the Thames Valley it is usefully milder than Bucks and the Flatlands to the E&NE. It's probably milder still down towards the South Coast (say, Hampshire)
IMHO he might better off heading Cirencester-way more to reduce the miles ridden around/below zero. Not quite so flat, I know, but just nicer miles!
But that could change pretty suddenly ...