Craigeedee - you are NOT asking your GP to change your file or falsify your records. You are asking him/her to clarify if you do or don't have asthma, and if you DON'T, you are asking them to ensure that that finding is clear and unambiguous on your medical records.
If they say that you might, or that it is unclear, you need to ask if any further tests can be done to prove or disprove whether you have asthma, so that the result can be given in your records. OASC will not give you the benefit of the doubt.
If they say that you do have asthma, you thank them and leave it at that. Trying to convince your GP to falsify your medical records is not a good idea.
I'd go and see your own GP for this. They won't mind; I sometimes wonder if GP surgeries are only full because of wannabe pilots checking their asthma history ...
