* Unless you are travelling on the day that a Dreamliner starts smouldering on the tarmac, your flight gets cancelled after a wait of 6 hours, then the helpful BA staff direct you landside via a gate which then exits you (at the end of a very lengthy) immigration queue !

True story, and by the time I realised where I had been directed, was of course past the point of no return. Luckily my own passport was in my bag and the nice gentleman at border control was satisfied that I was not trafficking (my own) children. It was 0200h at this point and I was indeed very grateful! This may have been one of the few situations where having checked bags could have worked to my advantage in making a speedier exit from the terminal

Admittedly, and hopefully, this scenario shouldn't manifest itself for the OP...