The Mousetrap, opened at the Ambassadors Theatre in London’s West End November 25, 1952. 
Agatha Christies murder mystery became the world’s longest continuously running play in history,  

In 1991, Royal Mail honoured this play in a Machin booklet. The play was highlighted as part of the Machin booklet pane, along with Christie’s Giant’s Bread. 

The Mousetrap and Giant’s Bread 
Queen Elizabeth II – Decimal Machin booklet 
Designer: Arnold Machin

The left pane reads: 

New generations have come to appreciate the whodunit skills of Agatha Christie since her death in 1976. Television adaptations of the Miss Marple and Poirot books have achieved critical acclaim as well as popular success. The crime novels themselves remain best sellers. On stage, The Mousetrap runs and runs and runs.

The right pane reads:

THE MOUSETRAP
In a sense, Queen Mary was the inspiration for the world’s longest running play. The Mousetrap. She was asked by the BBC how her eightieth birthday might best be celebrated on radio. The Queen, an avid fan of Agatha’s, requested that something by Miss Christic should be broadcast. Agatha was attracted by the idea and wrote what she described as ‘the little radio sketch called Three Blind Mice. As far as I know Queen Mary was pleased with it. The world was also pleased with it after the radio play, broadcast on 26 May 1947, was adapted into the stage version. By 1974 when the author was awarded the DBE and became Dame Agatha Christie, The Mousetrap had already been in the West End for twenty two years.