Passengers flying from Heathrow this weekend may be advised to use public transport rather than drive to the airport as environmental protests appear likely to focus on access roads.
About 250 protestors had gathered at a Camp for Climate Change close to Heathrow this morning, with 1,500 expected for a day of action at the weekend.
The airport has drafted in 2,500 additional security staff and 1,800 extra police to deal with the protest against the expansion of Heathrow and its contribution to global warming.
Protestors and legal observers complained at the use of anti-terrorism powers to stop and search all those approaching the camp.
The organisers insist they have no intention of trying to disrupt aircraft movements and point out the camp has widespread support from local residents. A spokesman said: "We are not going to break the perimeter fence or storm runways."
Airport operator BAA expects 1.5 million passengers to pass through Heathrow over the next few days. A spokesman said: "We're hopeful there won't be any disruption to the airport."
BAA won a partial injunction against the camp, but failed in its attempt to block up to five million members of various environmental groups from joining the protests.