Check-in staff are pretty much immune from all free upgrade requests and in many airlines they would have to justify it to their management.

Even with Op-ups the process is pretty much automated with the list determined in advance.

The days of a winsome smile, a nice suit/dress and some sort of heart warming story getting you into the pointy end are long gone.

If you are UK military I thought being in uniform when not on duty was discouraged.

And whilst the British people do respect those in the services they are unlikely to fawn over them like they do in the USA.