A protest by anti-noise campaigners who invaded one of the runways at Heathrow Airport was still disrupting flights this morning.
Thirteen members of the Plane Stupid action group cut a hole in the perimeter fence under cover of darkness at 3.45am.
The demonstrators chained themselves together and lay down close to one end of the northern runway.
Scotland Yard said nine people were arrested and taken into custody while efforts to remove the others continued.
The protest is likely to raise fresh concerns about security and the terrorist threat at one of the world's busiest airports.
Jets were able to take-off despite the occupation by using a shorter section of the runway.