City student among Stansted airport protesters

Activists broke into a secure area at around 3am, forcing the runway to remain closed for three hours.

Ryanair called for an investigation into why airport operator BAA had failed to keep the Essex airport "secure and open", saying the disruption to passengers was "unacceptable".

Today's protest by the Plane Stupid group was sparked by the Government's decision to allow the expansion of the airport with a second runway.

Activist Lily Kember, 21, a third-year anthropology student at Edinburgh University, said the group used bolt-cutters to get into a secure area around 55 yards (50m) from the runway.

Ms Kember, from London, said: "Being arrested is a terrifying prospect, but not nearly as terrifying as the threat of climate change."

BAA said protesters did not get on to the runway, but it was closed as a "precaution".

The runway had been due to open at 5am after maintenance work but remained closed until 8.10am, causing delays to flights in and out of Stansted.

Ryanair, the only airline to cancel flights, said: "Ryanair will be calling for an investigation as to why the BAA Stansted security has once again failed to keep Stansted Airport secure and open to the travelling public.

"It is unacceptable that the travel plans of thousands of passengers have been disrupted because BAA Stansted security have failed to remove a number of protesters."

Essex Police said 50 of those arrested today were held on suspicion of aggravated trespass, three on suspicion of attempting to gain access to a restricted area and four of conspiracy to commit a public nuisance.

A force spokesman said a detective superintendent will head an inquiry into the incident but added that security at Stansted was primarily the responsibility of the airport authority.