Greenpeace activists have climbed on top of a plane at Heathrow to protest against airport expansion.

The four protestors - two women and two men - crossed the runway to the Boeing 777 shortly before 10am after the plane had landed from Manchester.

Greenpeace said the four waited until all the passengers had disembarked from the one hour flight before walking through double doors at Terminal One, crossing an area of tarmac and climbing stairs onto the fuselage of the British Airways flight.

They unfurled a banner reading "Climate Emergency - No Third Runway" over the plane's tailfin.

Greenpeace said it informed airport operator BAA of the stunt as the protesters reached the doors.

Police are believed to be removing the protesters now.

The security breach comes as protesters gather for an anti-runway protest in Westminster later today.

In a statement released by Greenpeace, protester Anna Jones, 27, from Leeds, said: "I'm standing on this plane because our planet and the people who live on it are in danger.

"Climate change can be beaten, but not by almost doubling the size of the world's biggest airport.

"The scientists say we only have a hundred months to get emissions down, so we're here to draw a line in the sand and tell Gordon Brown his new runway must not and will not be built.

"I've never done a protest like this before, but people need to take a stand and tell the Prime Minister he can't ignore the science any longer."

The second female protester, Sarah Shoraka, 30, said: "Why are climate-wrecking planes flying between Manchester and London when the train only takes two hours?

"The government should stop giving billions of pounds in tax breaks to aviation and instead use that money to make our trains cheaper and better.

"The push for a third runway is being fuelled by totally unnecessary flights like this one."