2500 hrs on Albert.
AFAIR ASCOT stood for Air Support Command Operational Tasking.
In my time on the mighty Herc, ASCOT callsigns (4xxx for a Mk1, 5xxx for a Mk3) were only ever used for a/c doing Routes.
UK Training tasks such as MCT/CPT used a LYE C/S.
UK Op Training tasks (such as a LL air drop) used a 5 character alpha-numeric.