Booking Out
CAP 493 Section 1 Chapter 2 para 14
14. Booking-Out
Pilots who do not file a flight plan, either full or abbreviated, are required to inform the ATSU at the aerodrome of their departure. This is referred to as booking-out. The ATSU is to record the departure. No further action is required.
for the sake of completeness
10. Filing of Flight Plans
10.1 Flight plans fall into two categories:
(1) (2)
Full flight plans; the information required on Form CA48/RAF2919.
Abbreviated flight plans; the limited information required to obtain a clearance for a portion of flight, e.g. flying in a control zone, crossing an airway etc. filed either on the RTF or by telephone prior to take-off.
and
10.3 The destination aerodrome will be advised of the flight only if the flight plan information covers the whole route of the flight.
Busy ATSUs I would suggest prefer a booking out over the phone to alleviate RT workload and naturally be forewarned about potential movements.