When the RAF adopted the 1937 pattern webbing set in 1941 there was no perceived need for the entrenching tool cover in blue-grey. The RAF regiment were continuing to use the standard khaki set as issued to the Army and the rest of the RAF needed it for pistol equipment and guard duty so there was no need for an entrenching tool. In the post war period, however, it was decided to issue all members of the RAF, including the RAF Regiment, with blue grey webbing to better create an esprit de corps across the RAF and provide a clear visual distinction that they were not the army. As such entrenching tool covers started to be produced in blue-grey and today we are looking at one such example: 

The pattern chosen reflected the updates made to the pattern by the army in 1945 and so includes the extra strap to retain the helve that secured with a press stud under the right buckled securing strap: 

The RAF only bought very limited numbers of blue-grey entrenching tool covers and so they are distinctly scarce today. They all seem to date from the very early 1950s and this example is no exception, the stamps inside indicating a date of 1952: 

The Air Ministry stores code starts with a 23/ this being the code for webbing and field gear. With such limited production and presumably even more limited use, most examples found today are in mint condition like this example.  

If you would like to learn more about 1937 Pattern equipment, its production and use please check out my book Webbing at War Volume 1 1937 Pattern Webbing which can be found here.