Fifteen people have been arrested after campaigners against airport expansion staged a protest near Heathrow Airport.
A small group of people ran on to the M4 spur road and lay down in front of oncoming traffic, causing temporary disruption.
A number of others were arrested on suspicion of public order offences.
A Metropolitan Police spokesman said: "A planned protest is ongoing at Heathrow Airport on Saturday 19 November.
"A proportionate policing plan is in place.
"There have been 15 arrests for obstructing the highway and public order offences. Officers remain on scene."
As some people took arrestable action, other campaigners gathered on the flyover to chant "No ifs, no buts, no third runway" and "No more runways".
People of all ages were present to take part in the demonstration on Saturday which was organised by campaign group RisingUp!.
Placards reading "Heathrow expansion will destroy thousands of homes" and "Protect the planet, no more runways", were raised high as locals gathered in the cold to rally against airport expansion.
A spokesman for the group said: "The Government's decisions to expand Heathrow, despite mass opposition from local residents and the fact that doing so is incompatible with the UK's own laws on climate change, leaves us with no morally acceptable option but to resist.
"Only 15% of the British public is responsible for 70% of international flights taken in the UK and Heathrow largely serves international passengers who have a mean income of £57,000 per year.
"This expansion is being driven by the very rich at the expense of some of the poorest people in the world."
Neil Keveren, a resident of nearby Harmondsworth, said: "Democracy has failed us. Elected leaders have totally reversed the will of the people.
"As a direct result, the quality of life and life expectancy of the population here will be shorter. This is against our human rights and must be defended.
"Who is left to correct this injustice when our politicians will not? The answer is us - you and me."