I recall that, back in the 1980's, when the RAF had a morale and retention problem, they appointed the splendid Air Commodore Bobby Robson to review the problem and report. He bounded into the Officers's Mess Ante Room with a number of cracking wheezes. One of these was a form of ID Card for veterans.
Nothing wrong with that for, back in those days, it was a sentimental gesture and more a way of keeping the affiliation going.
I wouldn't trust the present civil service with an ID Card. They will put some kind of chip in it and use it for information gathering so they can keep tabs on ex serviceman.
Virtually (pun intended) everything that Whitehall touches these days involves gathering personal data.
So, I wouldn't touch an veteran's ID Card with the long end of a selfie stick.