Militants planning Heathrow break-in

Organisers are concerned that militant groups are determined to break through the airport's perimeter fence, infiltrate terminal buildings and leave hoax packages in arrivals halls.

The demonstration reaches its climax tomorrow with 24 hours of mass direct action by campaigners starting at midday.

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Tensions among climate change campaigners at Heathrow have reached fever-pitch

Hundreds of activists will march on the headquarters of airport operator BAA, the future Terminal Five and Heathrow's freight area in an attempt to stop perishable cargo such as fruit and flowers coming off flights.

But radical splinter groups are plotting more disruptive action, despite assurances from the protest camp that passengers would not be targeted.

Representatives of the Camp for Climate Change fear hardliners could cause a public relations disaster if they delay flights for holidaymakers on one of the busiest weekends of the year.

"The general consensus at the camp is that nothing should be done to disrupt flights and ruin people's holidays," one organiser said.

"But some are planning more extreme measures and although we would usually be on their side, we are worried that in this case it would be disastrous in terms of public relations.

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Heathrow protestors taking in the view

"There have been some big arguments.

"We want to be high-profile and embarrass the aviation industry but we don't want to disrupt ordinary passengers.

"I fear we may shoot ourselves in the foot on this one."

Protesters allied to the camp superglued themselves to the entrance of the Department of Transport in Central London.

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Tent city: the protesters sleep despite the noise of the jets overhead

Ten were arrested for aggravated trespass.

Other planned targets include the Royal Bank of Scotland, which has links to airport firms, and the home of Lord Soley, campaign director of Heathrow Future, a pro-aviation expansion group.

Around 1,000 campaigners are thought to have arrived at the camp near Heathrow, although this could swell to more than 2,000 over the weekend. There have been more than 30 arrests.

The protest is over proposals for a third runway at Heathrow and the wider issue of the impact of aviation on climate change.

Commander Jo Kaye, of the Metropolitan Police, has confirmed that known troublemakers are thought to be in or on their way to the camp.

"Some of these people have Reclaim the Streets heritage," she said, referring to previous anti-road demonstrations.

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Good weather for it: protesters rug-up at Heathrow

"If we frustrate them then they will go in for confrontation because their aim is anti-state."

The seven-day event, which began two days early, is being policed by up to 1,800 officers at an estimated £7million cost to the taxpayer.

Assistant Commissioner Tarique Ghaffur said any attempt to disrupt the airport could be dangerous because of the high alert level over the terrorist threat.

He added: "I would caution strongly against people attempting to break security at a site such as Heathrow Airport."

I don't believe this is your stop: police move on some of the protesters