CCTV descriptions showed the boy mingled with families moving through the airport on Tuesday afternoon. He went straight to the nearest aircraft boarding, the flight to Rome, where he was also missed during a head count on board.

“This is a serious breach. I treat security breaches very, very seriously. We are reviewing urgently...exactly what happened,” said transport secretary Justine Greening.

A statement issued, which said five members of the airport and security staff have been suspended following the incident, regards the mishap as "extremely serious".

However, the airline insisted that the boy had cleared security at the airport though without the necessary paperwork.

“It's not technically a breach of security. The boy posed no threat to the aircraft. He went through a security process,” defended airport spokesman Russell Craig.

The boy, who stayed on board the plane when it landed in Rome Fiumicino Airport and was flown back to Manchester on Tuesday evening. He had reportedly broken off from his mother at a shopping centre near the airport and plainly walked in the airport.