Police have moved into the climate change camp at Heathrow airport.
Officers began inspecting the site this morning after a complaint from the land owner, Imperial College.
Protesters gathered earlier than expected for a week-long protest camp designed to raise awareness about climate change and oppose the planned Heathrow expansion.
Chief superintendent Ian Thomas said 25 officers entered the Camp for Climate Action this morning after Imperial complained the protests were camped illegally on its sports grounds.
Camp organisers have been forced to allow four officers to stay on site and police have been photographing protesters.
Up to 2,000 people are expected to attend the camp near Heathrow airport and they will be overseen by 1,000 officers from Surrey, Thames Valley and the Met police and British Transport Police.
Heathrow owner BAA sought an injunction to ban activists planning direct action but the camp has also won mainstream support.
Local Liberal Democrat MP Susan Kramer has been a vocal opponent of Heathrow expansion and supports this week's activities.
"I'm going to get the message to BAA that opposition to airports is anything but fringe," the MP for Richmond told the Observer.
She continued: "It comes from mainstream law-abiding residents who have suffered long enough. My constituents are not 'nimbies'. They live under the flight path.
"We've been protesting about Heathrow expansion for years. We have lost any faith in consultations and any expectation that our voice will be heard...We say enough is enough."