Armed police arrested a man at Heathrow Airport today after he sprinted onto a runway clutching a bag, police said.
The second major security breach at the airport within 18 days happened shortly after 2pm on the northern runway of the London airport.
The man scaled a perimeter fence and ran towards a plane. He then dumped the bag and was quickly tackled by armed police. Officers seized the man, holding him face down on the grass at gunpoint, before leading him away.
There was a controlled explosion on the bag but police said no explosives were found.
Heathrow workers speculated that the man was a protester bent on causing disruption ahead of tomorrow's opening by the Queen of the airport's new Terminal 5.
Scotland Yard said anti-terrorist officers were aware of the incident but it was being dealt with by local police at the airport.
About two hours after the incident airport operator BAA said both runways had reopened. "Some short delays have occurred but we are expecting to return to normal later this afternoon," said a spokeswoman for BAA.
The airport is understood to have been testing security today ahead of the official opening of Terminal 5. The state of the art new building is a major landmark in the airport's expansion. Buckingham Palace said the Queen's visit would go ahead as planned.
The incident is the second time in recent weeks that Heathrow security has been breached. Greenpeace protesters walked on to the runway late last month and climbed on to a Boeing 777, unfurling a banner in protest against the airport's expansion.
Two days later members of the Plane Stupid group breached security at Westminster, climbing onto the roof and unfurling banners. Both groups denied involvement in today's incident.