How do I pay fees if I don't even land at the airport?
I fly in France and I had the same question. Apparently they use the aircraft registration to identify the owner. If you rented the plane from a club or renting company, the bill is going directly to them, otherwise they are going to try contacting you. If for some reason they didn't get your registration or if the airport was uncontrolled then you don't pay the fee. That's how it works over here, however I can't say if the same would apply in the UK.