Ruth Kelly and Department for Transport targeted by airport expansion protestors

Protesters pelted the Department for Transport's headquarters with paper planes today in a demonstration against airport expansion.

Watched by police, including an armed officer, the demonstrators, known as the Flash Mob, sported red T-shirts outside the Westminster building.

Before the action began at around 11am, Police Sergeant Paul McIntyre, based at Westminster, informed the protesters that the demonstration had not been authorised in accordance with the requirements of the Serious Organised Crime and Police Act 2005 - legislation which covers protests within the central London area.

However, Mr McIntyre said the protesters had to disperse by 11.10am - effectively allowing the demonstration to go ahead.

The T-shirts carried the message "No Airport Expansion", with the protest aimed at influencing the decision of Transport Secretary Ruth Kelly who is due to rule later this year on expansion at Heathrow Airport.

One of the organisers of today's protest, John Stewart, of the anti-expansion group Hacan, said: "I am very pleased with this demonstration and it shows the strength of feeling about expansion.

"The police decision today was a sensible one."

Today's demonstration was attended by Liberal Democrat deputy leader Vince Cable, whose Twickenham constituency in west London suffers from considerable airport noise.

Mr Cable said today: "Heathrow plays an important role in the economy but there is no economic justification for expanding the airport.

"Expansion would do much harm in terms of noise and emissions."

Mr Cable described the 2005 Act as "grotesque" and "a misuse of the legislation".

A Department for Transport spokesman said: "Everybody has a right to peacefully protest but that must be within the law.

"We had a consultation on airport expansion and we are now considering views from 70,000 people and expect to make a decision on Heathrow later this year."

Anti-expansion protest group Plane Stupid said its members had played aircraft noise through the letterbox of Ms Kelly's London Docklands apartment this morning.

They said that after 15 minutes they were interrupted by the Transport Secretary's husband.

They left him a letter which said: "We do hope that you will keep this early-morning wake-up call in mind when you decide the future of Heathrow after the summer recess. All the best, your friends at London Plane Stupid."

The group said they had left peacefully but were chased by Ms Kelly's husband.

Plane Stupid spokeswoman Elizabeth Baines said: "It's incredible. Tucked away in her posh London flat I can now see why it is so easy for Ruth to ignore the concerns of west London - the expansion of Heathrow won't threaten her quality of life.

"Labour have realised how controversial a decision in favour of the third runway will be, so have pushed back their decision until after the summer recess."

The protest coincided with a similar protest, organised by Plane Stupid Manchester, outside Ms Kelly's home in Bradford, West Yorkshire, this morning.

Matthew Knowles, spokesman for the Society of British Aerospace Companies, said: "As many people fly off on their well-earned summer holiday it will strike them as unfair that a small unrepresentative band of people want to take that away from them.

"New planes coming into operation now are much cleaner and will be ones that are flying at the time that the new runway is planned. For example, the Airbus A380 (superjumbo) produces less carbon dioxide per passenger kilometre than the average car that is exempt from the London congestion charge on environmental grounds.

"Heathrow is operating at maximum capacity at present. Without expansion we will continue to see aircraft circling before landing, producing more CO2 than is necessary because of this opposition to a larger Heathrow. With a third runway flights will be able to land directly rather than circle, producing less CO2 than they do at present."

Jenny Jones, a Green Party Member of the London Assembly, who was joining the Department for Transport protest today, said: "Expansion of Heathrow would lead to spiralling CO2 emissions, unacceptable noise disturbance for over two million Londoners and worsening air quality, yet the economic benefits would be highly questionable. Expanding Heathrow does not make economic or environmental sense."