ATS.TR.225 Responsibility for control

(a)A controlled flight shall be under the control of only one air traffic control unit at any given time.

(b)Responsibility for the control of all aircraft operating within a given block of airspace shall be vested in a single air traffic control unit. However, control of an aircraft or groups of aircraft may be delegated to other air traffic control units provided that coordination between all air traffic control units concerned is assured.