Police arrested a group of Greenpeace activists who climbed on top of an aeroplane after it landed at Heathrow Airport.

Their demonstration ended at around 11am on Monday, just over an hour after they breached security to hang a banner on the tail fin of an Airbus A320 in protest against the London airport's expansion.

The four protesters are being held at the Metropolitan Police's Heathrow station, a spokeswoman for airport authority BAA said.

Greenpeace said the group waited until all passengers had disembarked from a British Airways flight from Manchester to Heathrow before clambering on to the roof. The banner the two male and two female activists briefly attached to the plane read "Climate Emergency - No Third Runway".

One of the protesters, Anna Jones, 27, from Leeds, spoke to reporters during the demonstration, saying: "I am 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."

Greenpeace said the group managed to dodge security simply by walking through double doors at the terminal, crossing an area of Tarmac and climbing stairs on to the fuselage.

The ease with which the activists made it into an heavily restricted area prompted some to voice concern about security at the airport. Paul Kenny, general secretary of the GMB union, said: "We need to have an investigation to establish if the escalating use of agency staff at UK airports has played a role in creating this security lapse."

The protest came two days before the end of a Government consultation into Heathrow expansion. Greenpeace claimed the process of consultation was "fixed".

A spokeswoman for BAA Heathrow said: "There is an important debate to be had regarding airport expansion and BAA respects people's democratic right to protest lawfully. However, direct action on the airfield is unlawful and irresponsible."

Flights departing from and arriving to Terminal 1 remained unaffected by the incident.