The stunt, which started at 7.40am, left long tailbacks for those going to terminals 1, 2 and 3 and was timed to coincide with today’s parliamentary debate on UK airport expansion.

The Telegraph has reported the protest began when three activists blocked off both lanes of the tunnel by parking a van emblazoned with David Cameron’s election pledge "No Ifs, No Buts: No Third Runway" across it.

Police were alerted to the incident at 7.42am and arrests were made soon after. The incident caused large amounts of traffic to build up at the airport.

Plane Stupid spokeswoman Cameron Kaye said in a statement on the group’s website: “Airport expansion would wreck the legally binding Climate Change Act, risking wiping out 55% of species this century and displacing 75 million more people from their homes by 2035.

“If aviation growth isn’t reduced, by 2037 aviation alone could emit all of the carbon it’s safe for the UK to emit. The government needs to choose: build new runways or stop climate chaos: it’s that simple.

“There is already airport capacity for families taking their yearly holiday. New runways only benefit the 15% of flyers who take 70% of our flights, cooking our planet.

“These are rich frequent leisure flyers. The most reliable predictors of frequent flyer status are a household income over £115,000 and owning a second home abroad, but it’s the poorest people who suffer most from climate change.”