Have PM'd HA and BJ.
Just as an update and please forgive the lack of technical knowledge, I am sure some admin guru will be able to add to what I put here.
Medical discharge pensions are worked out from a set of Tables, and are slightly different (marginally better) than you would get as far as the standard Pension on departure, I'm not talking about tax status or index linked here, just the amount. The only problem with that system for PA Spine individuals is that there are no tables that cover the PA Spine, meaning when you ask the Forces Pension Society for help they can only work out your length of service and rank. This means with 30 years service as a Flt Lt you get a very different figure to 30 years Flt Lt and near top rate PA. However the good news was that after a significant amount of head scratching at High Wycombe and Glasgow my pension was awarded at the rate it would have been if I was leaving on normal grounds, with a few minor medical benefits as well.
Hope that is of some help to someone.