MEDICAL - DO IT NOW!
Probably not a problem, but if there is a problem, find out before you spend the whole bankroll on the training.
There are 2 kinds of Medical Requirements, have a look at the Civil Aviation Authority Website for details. Your own doctor can certify that you meet the requirement for a "National Pilot's License"....for example, if you qualify to drive a truck, you are fine to go.
And there is the proper Aviation Medical, for the Private Pilot's License, which enjoys more privileges; this one needs an Aviation Medical Examiner to check you out. No dizzy spells? reasonably sane? wear corrective lenses? (varifocals not recommended!).
Your instructor/flying school could recommend a friendly AME. But the CAA information on the internet is very helpful and detailed.