There are quite a few. The largest population is probably in Eire, but I know of at-least one in Austria, and believe that there are a few in France, Spain and Portugal.
You don't need the permit air test to be done in UK airspace so long as the permit hasn't expired. So, basically, always get the permit revalidated before it expires, or get the aeroplane back to the UK before it expires to then get it done, otherwise you may have a struggle.
In Eire, the IAA issue a validating "Flight Permit" to make it legal to fly, basically issuing a local permission on the back of the UK PtF. What other countries do, I know less about.
G