A flight plan does not constitute booking out.
In the UK VFR flight plans generally are ignored as they do not require to be closed and do not usually contain the required info for SAR. eg POB endurance and contact phone Nos. Often the arrival or departure airfield will not have an AVPEX terminal. (and probably fewer will have in the future)
The only time a VFR flight plan is required is when intending to cross an international boundary.
The booking out procedure at my local licenced field is written in to the airfield ops manual and SMS manual. This has been in place for many years due principally to the extremely inhospitible terrain nearby.
As Helen49 says in her very sensible posts licenced airfields are required to log all movements and arrival and departure information. Several agencies may have an interest in this information.
D.O.