One in Cornwall and one on the Orkneys should be enough.

It's more of a local British problem...

Any blueprints for these settlements we can use?

Land’s End and Marshall Meadows Bay should suffice.

Although at this rate, Northumberland will be accidentally seceded to a newly independent Scotland, and the entity of Cornwall will become part of an independent Wales.

The British did this a while back when their Empire still looked strong - the Foundation was North America. The silent sleeper cell second foundation is probably New Zealand. Unfortunately, Boris Johnson a.k.a the Mule came along.