More than 100 demonstrators at the Heathrow climate change protest camp have tried to block police officers trying to enter the site, amid growing signs of tension.
According to media reports, up to 30 officers were blocked by a human chain of protesters as they attempted to enter the site, Tuesday night.
Protest organisers are accusing the police of heavy-handed tactics. According to the Camp for Climate Change Website
police have also stopped and searched some people going to the camp, under anti-terrorism legislation.
Organisers estimate 550 people have joined the camp near the village of Sipson by last night, accompanied by a host or reporting media.
Camp organisers have also confirmed that they have sent an email urging activists to bring smart clothing to blend in with ordinary workers at Heathrow ahead of the main protest on Sunday.