Certainly in use in RAFG in the early 70's.
Are you positive
VM? I was at Gut '76-'78 and don't remember them then.
And they weren't the same as the '50s "Aerograms", not least because they were free! (
VM, having just re-read your post [Doh!] and you mention a stamp. The blueys I mean were totally free - no stamp required. Perhaps that's the confusion?)