Eleven year old shopping with mother. Bored. "Fed up with this. Let's go to Rome," he thinks. "Now, how do I get there? Oh yes. Number xxx to the airport, and then Jet2 from Terminal One. I really want to lie on the floor of the Sistine Chapel and look up at the ceiling."
He waits for his opportunity. Mother is distracted by the exciting contents of the freezers.
"Now's my chance," he decides.
Boy boards bus. Boy gets off bus at airport bus station. Boy walks or takes bus from airport bus station to terminal one. Boy walks straight through departures to security checks, somehow evading boarding pass examination at entrance to security area. He takes off his belt and shoes, puts them in the tray, goes through the arch, collects them, and makes his way to the departure area.
He checks the board, goes to the appointed gate, and gets on the plane, somehow avoiding the boarding pass and passport check. Jet 2 has allocated seating, but somehow he sits in a seat which has not been purchased online or allocated at check-in.
Come on folks. Waken up and smell the coffee. This was a put up job. There was a huge spread in the Sun the next day. He may have slipped through but it was made easy for him. I'll bet a pound to a dirty penny there was some kind of journalist on the flight keeping an eye on him. I'll also bet money has changed hands in the matter.