I did one about 3 years ago and if I remember right (which, to be honest, I probably don’t!) I think my GP surgery wanted to charge for it, though I can’t remember how much. But I just got my neuro to do it instead, and she signed it without any bother, so give your neuro a call and see if they’ll do it for you.
Hope it all works out - I raised about £1,500 (my employer does a £for£ scheme, which bumped up the total loads), and it’s one of the best things I’ve ever done. If you can afford it, I highly recommend paying to have a DVD & photos done of it. I wasn’t going to at first as it’s a bit pricey, but a few people clubbed together & got it for me as an early Christmas present, and I’m do glad they did, as I can re-live the experience whenever I want, and I’ve got a great framed photo of me saluting the camera during the freefall (you can watch it here - The day I jumped out of the Sky - YouTube). Just make sure you prepare something good to say to the camera instead of being put on th espot like me & looking like a bit of a numpty!