A government decision on Heathrow's expansion is due this year
Protesters have thrown paper planes at the Department for Transport's headquarters in a demonstration against the expansion of Heathrow Airport.
The Heathrow Association for the Control of Aircraft Noise (Hacan) have been demonstrating against a planned third runway and a sixth terminal.
Earlier another group played aircraft noise through the east London letterbox of Transport Secretary Ruth Kelly.
A government decision on the airport plans is due later this year.
The demonstrators sporting red T-shirts - carrying the message "No Airport Expansion" - protested outside the department's building in Westminster in central London.
Before the action began at around 1100 BST, police informed the protesters 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.
Protesters were ordered to disperse by 1110 BST - effectively allowing the demonstration to go ahead.
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."
Thursday's demonstration was attended by Liberal Democrat deputy leader Vince Cable, whose Twickenham constituency in west London suffers from considerable airport noise.
He said: "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".
Earlier, protest group Plane Stupid played 15 minutes of aircraft noise through the letterbox of Mrs Kelly's Docklands apartment. They said they left peacefully but were chased by Mrs Kelly's husband.
It coincided with a similar protest by Plane Stupid Manchester outside Mrs Kelly's Bradford home.
A Department for Transport spokesman said: "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."
Last week Colin Matthews, the head of Heathrow operator BAA, said the "jam-packed" airport needed a third runway to remain competitive globally.