Can anyone help with a war pension query.

I have a client who left the Army in 1966. His discharge notice says the reasons are "below physical standard", the client suffers from cronic anxiety and depression. Long before I got involved (about a year) the client put in a claim for a war pension and was turned down on the grounds that his current condition was not related to his time in the service (it was also turned down in 1966). I pointed out that as there was a lot of stigma surrounding mental health issues back then, that "below physical condition" was often used instead, I also pointed out that the client was admitted to a army hospital in 1966 for 'Anxiety State' this was shortly after he had served in Brunei and Borneo(fortunately the client had kept his F24 medical cerificate from 1966 which states this), and shortly before he left the service. War Pensions have now said he had a pre existing mental health problem before his service in 1966, which the client denies, and I have contacetd them to ask for prove. War Pensions said I could do a late appeal of the 1966 decision, but would need to quote grounds. Has any one got any advice or preferably case law that I can use for this.

Many thanks

Should have mentioned that i understand if the client's pre existing condition was stress and anxiety related then my case is just about non existant, but i have my doubts if it is relevant condition, as the client would have probably remembered it. My query was whether War Pensions can get away with just using condition on discharge notice, and completely ignore the condition that client was admitted to army hospital for, shortly before leaving service.