When you arrive at your drop zone for AFF ground school, the first session will be to complete the paperwork, including the medical aspects.
Under the USPA system you could complete a medical declaration which asks you to state that you have never had any of the conditions which are listed on the form. You may already have an FAA certified medical and if you do, this meets the requirements fully.
The BPA system will also require you to complete a declaration and a copy of the current form (the 114a) is attached here (click the link) so you can see what you’ll need to sign up for. You should be aware that you can only sign this if you are between the ages of 18 and 40 years old. If you are aged 16 to 18 you can still sign, and you will also need a parent or guardian to sign in addition. You won't be allowed to use another kind of medical (e.g pilot medical) and you must use the BPA form. I mention this just to save you some delays on the day you come along to start your course or do your skydive.
If you are over the age of 40 years on the day you start your accelerated free fall ground school, your signed medical declaration is not enough and you’ll need a full medical certificate, signed and stamped. The simplest way is to see your own general practitioner, who can usually do this for you although it’s not covered by the NHS system. You’ll usually be asked to pay for this before your doctors office will book an appointment and it’s a good idea to take along a full copy of the certificate to the reception of your GP.
Most GPs nowadays are fairly well clued up on this and they charge a reasonable fee (between £15-£40). I’ve heard of some however, that discourage these by charging high prices and guess what? They are allowed to do this. In this case, I suggest you just ‘shop around’ and find a doctor who is used to doing this kind of medical. They’ll usually charge between £30-£50.