The boy was safely back in Manchester on Tuesday evening, met by his mother at the airport after completing the round-trip of 1,300 miles aboard the same aircraft he had boarded hours earlier. In Rome, he was held aboard the aircraft, operated by the budget airline Jet2.com, while he was questioned by Italian police and border officials, who cleared him for the return journey.

Airline officials said he told them that he ran away from his mother during a trip to a shopping center near the airport, then made his way to the aircraft by tucking in with other children as they passed with their parents through the successive airport controls. In all, Liam passed through a passport and boarding pass check on entry to the airport’s departure area; a scanner area where all passengers and their hand luggage are individually screened; another passport and boarding pass check at the gate; a boarding pass check on entry to the aircraft; and a head count by cabin crew aboard the plane.

Concerns about a possible aerial hijacking of the kind that led to the terrorist attacks on New York and Washington have been high among Olympic security planners. They have placed helicopter-borne snipers and supersonic fighter jets on 24-hour alert around the Olympic Park in east London, and positioned antiaircraft missile batteries on high rooftops overlooking the park. On Tuesday, a Typhoon fighter was scrambled after what turned out to be a false alert about an airliner bound for Heathrow Airport that failed to respond to ground controllers.

The British army has stepped in at the last minute with nearly 5,000 extra soldiers, on top of 13,500 already in the security plan, to take the places of thousands of private security guards that the main Olympic security contractor, the G4S company, failed to deploy on time. Through gritted teeth, government officials and Olympic organizers have said that the games will be safe and secure, and that spectators and athletes have no cause for alarm.

Spokesmen for the airline that flew Liam to Rome said they had fired several people on the airline’s security staff, and tightened checks at every stage in the boarding process. The transport minister, Justine Greening, said she had ordered a full report.