By Jonathan Davies

Planes were grounded at Heathrow in the early hours of Monday morning after climate change protestors managed to get onto the runway.

Thirteen members of the Plane Stupid group, which opposes plans for a third runway to be built at Heathrow, cut the fence and chained themselves together on the northern runway at around 3:30 BST.

The runway was closed for around three hours, resulting in 13 cancellations and numerous delays. Heathrow has advised passengers to check with their airline before travelling.

Six of the protestors have been arrested on suspicion of Aviation Act offences, police said. But some protestors are still at the runway, with police remaining in the area until they have been removed.

"We are working closely with the police who are dealing with the incident," Heathrow said in a statement.

"Both runways are open although there will still be delays - we are sorry for the disruption to passengers.

"Our priority remains to ensure the safe running of the airport."

In a video posted online, a police officer is seen talking to the protests. He said: "As a consequence of you being here, you are causing severe disruption and it will be in the millions of pounds because it will take us a while to remove you.

"The cost will be in the couple of millions. The airport will attempt to make a civil recovery."

Ella Gilbert, one of the activists on the runway, said: "We want to say sorry to anyone whose day we've ruined, and we're not saying that everybody who wants to fly is a bad person.

"It's those who fly frequently and unnecessarily who are driving the need for expansion, and we cannot keep ignoring the terrifying consequences of flying like there's no tomorrow."