All correct Geoffers!
I think it was a 'B' series C28 in the L-1 which, for clarity, was marketed as the 206L1 LongRanger II.
Thanks to 76Fan I see now that LRII went straight from CSE to Castle.
As you may know, Roy Flood bought his first 206 from Ferranti (G-BAKX) in 1978; I say Ferranti, it was in fact Mohammed Al Fayed's ex-craft which had been managed by Ferranti and which had a Ferranti interior fitted.
Thanks Wiggy (for the post below).