Originally Posted by NickB

Somebody who has already gone through airside in an area of the airport where there are international departures and who leaves the controlled area (i.e. airside) otherwise than on a plane. In principle, you are not allowed to do it without HMRC authorisation. HMRC policies seem to vary from airport to airport. For instance, at MAN T1 a few years back, they would not let me through unless accompanied by a representative of the airline I was flying.