Can't say for sure as it works differently in Canada, but I checked with a Transport Canada regional medical office for a friend with a withered arm. The doctor said that a medical flight test would be required.
I took him up on a flight and let him fly once at altitude to see how he got on -- quite reasonably.
He then went off to a local flight school to start lessons, told the instructor he was working on his flight test (leaving out the word
medical
) and did the taxi and takeoff. The instructor clued in sometime after rotation
so do be careful about saying
medical before flight test if that's what you're talking about.
If you phone an aviation doctor in the UK, he will be able to give better information.