Hiya, having done this several times in the past, ensure the wording is exactly as the template. get your doctor to sign/stamp and date it (again check the website as I think it needs to be within a certain date window before the race).
Some doctors will charge, others won't and it is only as good until you walk out of the surgery as they won't/can't guarantee anything.
I know some people have just got their mates to sign the letter, as all they check is that is is signed by a "doctor".
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