DOZENS of passengers heading from Scotland to Heathrow were delayed as activists chained themselves to railings and lay on the tarmac at the London hub in protest over plans to add a third runway.

A spokeswoman for Glasgow Airport said the early morning British Airways flight to Heathrow suffered a "minor delay" of less than an hour as a result of the disruption caused by campaigners from climate change group, Plane Stupid, who invaded the runway at 3.30am.

One flight was cancelled from Edinburgh Airport with passengers facing delays of up to an hour on the flights which did depart for Heathrow.

The demonstration on Monday caused delays for passengers around the world and 22 outbound flights were also cancelled.

Nine of the 13 demonstrators were arrested by police.

The stunt comes follows a report by the Airports Commission which recommended building a third runway at Heathrow.

Louise Rogers, 35, and Ciara Lalor, 34, had their flight home to Dublin cancelled.

Ms Rogers said: "It's affecting an awful lot of people's lives. I'm not one bit impressed. They should be shot with rubber bullets."

Ms Lalor said: "They've disrupted so many people. They shouldn't be allowed. Get the fire engine out and hose them down."

Travellers also took to Twitter to vent their frustration.

Other flyers were more sympathetic to the protesters, with Eamonn Maguire posting: "As someone sitting waiting at Glasgow Airport about to board a flight to Heathrow: fair dos."

A video posted online showed several activists chained together and being spoken to by an officer who is heard saying that the airport "will attempt to make a civil recovery" from them over the disruption to flights, which is likely to run into millions of pounds worth of compensation.

Environmentalists opposed to the third runway say it will make it harder for the UK to reduce air pollution and greenhouse gas emissions.

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.

"No ifs, no buts, no third runway. And we mean it."

Afzal Ashraf, a consultant fellow at defence and security think-tank the Royal United Services Institute, said incident "does raise questions" about security at the airport, which is the busiest in Europe and the third busiest in the world.

"If they did manage to get to a runway before being apprehended then there is a bit of an issue," he said. "If a terrorist group came up to the fence it would take a few minutes to cut through. It's very easy to get to a fence before the police are able to react."

A spokesman for Heathrow Airport said: "This morning a group of people staged a protest on the northern runway. These individuals have since been removed by police.

"Both runways were operational throughout, although there have been some delays and a few cancellations - we are sorry to those passengers who experienced disruption this morning.

"The safety of our passengers and the smooth running of the operation is paramount. Anyone who breaks the law and interferes with the safe operation of the airport can expect to face legal action."

The protest coincided with fresh complaints from the Teddington Action Group (TAG), local residents who oppose to the expansion, over Commission chairman Sir Howard Davies' impartiality.

They claim he never declared links to GIC Private Ltd, which own a 11.2 per cent stake in Heathrow, and Prudential PLC, which bought hotels around Heathrow through its investment vehicle, M&G Real estate.

Sir Howard is set to appear before the House of Lords economic affairs committee on Thursday to be grilled on his decision to recommend at third runway at Heathrow.