Sleap was used as a satellite to Shawbury in the early-mid '60s; I recollect that it was some kind of approach training, and club flying was stopped during it. Was it with Piston Provosts? Jet Provosts? The word was that you could get paid for riding along as safety observer ("HCAS") while P1 was fixated on the panel. But I don't know if that continued until the '70s.