Craigeedee,
The misdiagnosis line is a good one. It might also help if you knew exactly what was written.
If you have not got a copy of your notes you may submit a 'subject access request' to your GP. As we are talking dark ages the cost may by no more than £50 IIRC. Your GP's Data Controller, usually the GP, has to respond within 21 days (a Government promise) although the FOI stipulates 40 days.
It is possible you might get a holding reply first.
Incidentally you can look at your records for free. If you were happy just for the relevant time period then thi smight reduce the costs. The GP is also required to explain any medical terms and abbreviations for instance NFL or NFN which are Normal for Lincolnshire - slow and rural or Normal for Norfolk - dim. These terms are no longer used now that you have the right to see your own records but you may find them in earlier notes.