A 12-year-old Dutch boy has sparked a major security inquiry at Heathrow Airport after he boarded a plane unaccompanied without a ticket, according to UK media.

The boy was only spotted when a stewardess asked to see his boarding pass after he got onto the British Airways flight to Los Angeles, the Daily Telegraph reported.

The plane was delayed for four hours while all passengers were ordered to get off and go through a second security check on Sunday evening. The boy refused to leave the aircraft until he was led away by police.

British police confirmed that the stowaway was an ‘unaccompanied minor’ who was ‘not a UK national.’ He is believed to have arrived at Heathrow as a transit passenger.

British Airways and Heathrow both apologised for the delay and the airport said it was investigating how the boy passed through security checks unnoticed.

A spokesman said: ‘The individual did not represent a security risk and, purely as a precaution, the aircraft in question was re-screened and has since departed.’