Hi there. Just a wild guess but Pre-stamped and supplied by FPO counter staff? Looks interesting.

Thank you Michael. I shall endeavour to seek out the title you recommend, sounds very useful, thanks. I enjoy reading around the subject although I'm highly unlikely to ever exhibit anything.
Kind regards
Matt Gibbs

Thank you very much for those links Peter.
I've had a fair bit of time away from collecting as my mother passed away but I'm working on a few bits of research again now.