
On average, charity parachute jumps cost the National Health Service 14 times more in servicing the injuries the luckless parachutist incurs than they raise in sponsorship.
Leaving the customs union has a similar effect. The United Kingdom loses, at a stroke, every existing trade deal it has as part of the European Union, including the coming deals with Canada and Japan, and in theory gains the right to strike as many trade deals as it wants.