requires a pilot intending to make a flight to inform the Air Traffic Service Unit (ATSU) at the aerodrome of departure,
From a standing start, not knowing UK regulations, and having never "booked out" in reading the quoted regulation, I would only feel obliged to inform the ATSU at the aerodrome of departure. If the aerodrome of departure had no ATSU, I would notify a responsible person of my choosing, and go.
As I drive my car, I fly my 'plane as a private matter. If I want a third party to know where I'm going, I'll file a flight plan. Otherwise, it's a flight itinerary with the private person of my choice. But, that's Canada for you....