There's an ongoing discussion on war pensioners/AFCS recipients and related items HERE.
I've not had any problem with HMRC.
In my area the local SS (Social Services is how they describe themselves) at first did not wish to recognise me as disabled even though I am in receipt of 50% war pension and WPMS (which they appeared not to have heard of), and wanted me to sign on to their "disabled register" and carry a photocard.
After some discussion, and the suggestion that they might like to be as able-bodied as I, along with a letter of support from WPWS (war pensioners welfare service) they relented.
To be fair, this is not the case in all areas though, but there are some jumped-up college trained (though apparently not educated) SS staff who like to make life difficult.