Many [many] moons ago, I was working in the Flight Briefing Unit at Manch. We had a visit by a couple of HM Customs Officers.
HMC "Right sir, it is true that in this area we have Manchester and Liverpool Airports."
Me "Well...yes for Airliner types"
HMC "Pardon"
Me "Well, there's Barton,1/2d Green, Sleap to name but a few"
HMC "They DO file a flight plan, though?"
Me "Sometimes.....Then there is the guy who 'books out' to Kent, and goes via Belgium"
HMC is getting paler by the second
Me "Don't forget all those 'Farm Strips' they don't speak to anybody"
Him and mate left PDQ. Was it a coincidence that "Customs Regulations" were relaxed a couple of years later?
watp,iktch