What happens after you have told DVLA about your medical condition : Directgov - Motoring
This is the page that gives info about how DVLA deal with matters when an individual advises them of medical conditions. You can see from this that they may contact your doctor and/or consultant.
If they have informed you that your only option is to appeal to a magistrates court then I would start the process now. Get all the evidence you need from your GP and consultant to prove your case. I would also do a subject access request to DVLA to see exactly what information they have on you relating to this matter.
This document may be useful to you:-
http://www.dvla.gov.uk/media/pdf/medical/aagv1.pdf
Here is a court case in Scotland detailing an appeal against revocation:-
GILLIAN MARGARET CARRUTH v. DOCTOR LINDA CLARKE, QC ADVOCATE GENERAL, 22 November 2005, Sheriff R.S. Vaughan
And from Section 100 Road traffic Act 1988:-
100.—(1) A person who is aggrieved by the Secretary of State's— - (a) refusal to grant or revocation of a licence in pursuance of section 92 or 93 of this Act, or
- (b) determination under section 99(1)(b) of this Act to grant a licence for three years or less, or
- (c) revocation of a licence in pursuance of section 99(3) of this Act,
or by a notice served on him in pursuance of section 92(5) of this Act may, after giving to the Secretary of State notice of his intention to do so, appeal to a magistrates' court acting for the petty sessions area in which he resides or, in Scotland, to the sheriff within whose jurisdiction he resides.
(2) On any such appeal the court or sheriff may make such order as it or he thinks fit and the order shall be binding on the Secretary of State.
(3) It is hereby declared that, without prejudice to section 90 of this Act, in any proceedings under this section the court or sheriff is not entitled to entertain any question as to whether the appellant passed a test of competence to drive if he was declared by the person who conducted it to have failed it.
You should be able to find out more information from your local magistrates court. If you are a member of the RAC or AA they may be able to assist you and going to the CAB is an option.