When aircraft are flying within controlled airspace such as airways, they are usually under the positive control of ATC. This means the controller will issue positive intsructions to the aircraft such as speed, level and heading control. Airacraft being transferred from one unit to the next remain under positive control and details of the flight are co-ordinated prior to handover by the controller.
From
UK Air Traffic Control
The CAA website contains a document relating to Radar Control Service in Class D airspace which was withdrawn in 2003. I suspect it's obsolete!