(1963, Terence Longdon, Harry Fowler)
“British 'B' prison escape drama, features Karrier minibus 883CPP throughout; carries fleet number 3 and looks to have had a round fleetname vinyl covered up or removed.” (thanks Jon Price)
Martin advises this Karrier 98A/Reading was with Brookmans Park Motors, and I'm confident it's the same bus seen in Village of the Damned, made in 1960. In the latter, the bus appears with the distinctive 'BPM' fleetname on the side.