ASCOT Callsigns were formed as an acronym of Air Support Command (ASC) and Operational and Training (OT) to manage the big AT Fleet that meandered its way to service the pink map in the late 60s and early 70s. Alas the pink world started shrinking in mid 70s but the legacy has lived on.
ASC was formed on 1 Aug 1967 to absorb the then Transport Command and certain elements of other ac that could be deployed overseas in a tactical air power effort.
The call-sign was the brain-wave of a corporal in HQ ASC at Upavon where they controlled the many different types of AT ac. He probably received £25 for this 'invention' but the copyright would have fetched him millions.