Check JAR FCL 3 appendix 11 it will give you the guidance.
If you are dealing directly with CAA at Gatwick then they will be only too glad to help you, contrary to popular belief they do try to keep you flying.
Class 1 may be more tricky, again take the advice from Gatwick but be prepared to have an MRI private cost around £400 as the CT is unenhanced.
Best of luck