It is possible that it served at Biggin Hill with a different body and was later converted to a turntable ladder. It isn’t that unusual for fire engines to be rebodied or adapted by various owners over the years.

It does happen, but these K4s were built with the turntable ladder in 1943 for the NFS on a Home Office order which would seem at odds with the Biggin Hill suggestion. I suppose that it could have been based at Biggin, but with the NFS rather than with the RAF? There are thought to be something like 12 of the 50 built still extant.