I found this amongst them. It was not dated but from memory I do recall saving it two or three few years ago.
I thought it very amusing at the time, but obviously Royal Mail did not see the funny side. Read on to see what was reported in the Press:
Artrepublic, an English enterprise, which sells so-called 'artprints' - one should see them as a kind of artistic posters - ran into trouble with the British postal services. The problem was with the stamp, it was very similar to that of the well-known Machin definitive type.
On the Artrepublic poster version, HM Queen Elizabeth II is wearing a gas mask. The 'artprint's' title: was: "Black Smoke, Stamps of Mass Destruction".
Royal Mail threatened to sue the company if it did not withdraw the posters from the market. Something which Artrepublic immediately did.