By Jon Kelly BBC News, Heathrow

Claire Blatchford, 20, is a full-time protester and has joined the camp

But the lines of burly police officers around the site, not to mention the 747s roaring overhead, give a clue as to the true purpose of this gathering.

Flanked by Heathrow Airport on one side and west London's outer suburbs on the other, this is an unlikely setting for an impromptu eco-village.

Environmental campaigners have assembled here not just to oppose a third runway for the airport.

With their compost toilets, wind turbines and leaderless command structure, they are also keen to demonstrate that an alternative, more sustainable way of living is possible.

But despite the inevitable privations they face, not all the protesters conform to the typical eco-warrior stereotype.

Brenda Hatton, 60, says she is protesting for future generations

Brenda Hatton, 60, a retired head teacher from central London, says she woke up to the issue of climate change after her 29-year-old son began studying geography at university.

"I'm not here for me - I'm here for my children and my grandchildren," she said.

"It's all been very good-natured so far. I hope there won't be any trouble, and if there is it won't be because of the people on the camp."

Terrorism Act

The police, however, are not so sanguine.

Some 1,800 officers have been mobilised, almost matching the 2,000 campaigners who are expected over the coming week.

All vehicles approaching the site are searched under section 44 of the Terrorism Act and photographs are taken of anyone who enters.

Campaigners - who insist their protest will be peaceful - complain that the police approach is heavy-handed.

"We've had to shuttle all the supplies in here using wheelie bins. It's not exactly high-tech," laughs volunteer Tony Chambers, 35, a forestry worker from Ceredigion, mid-Wales.

Talks will be held on topics like carbon offsetting and wind energy

"But we've managed to set everything up without any problems so far. The attitude of the authorities just smacks of desperation, really."

So far only about 250 activists have gathered at the camp, but organisers are preparing for an influx they expect to join them as the week progresses.

There are clear protocols to follow.

Protesters pitch their tents alongside others from the same area - Oxford, London and Nottingham already have settlements, each with their own kitchen serving vegan, organic food.

They say they are here to learn as well as speak out.

More than 100 workshops are due to be held on subjects like carbon offsetting and building wind turbines.

But despite their leaderless structure - where all decisions are taken by consensus at regular meetings - reporters must follow the protocol of going through a dedicated media team before setting foot on site.

Camaraderie

On Sunday - expected to be one of the airport's busiest days of the year - they plan "mass direct action", although all insist this will be non-violent and there will be no attempt to blockade runways.

I can't tell you what will happen, because we'll decide collectively when everybody gets here, but it will be a peaceful protest Gary Dwyer, protester

"We have to do something," says Gary Dwyer, 34, a care assistant from Southport, Merseyside.

"Climate change is the biggest issue we face and we haven't got long to act.

"I can't tell you what will happen, because we'll decide collectively when everybody gets here, but it will be a peaceful protest."

As they wait for reinforcements to arrive, the campers say they are enjoying the camaraderie of pulling together and setting up their temporary community.

"It's been fun so far - I've been topping up my tan while I work," laughs Claire Blatchford, 20, a "full-time protester" who has spent four months at a peace camp outside Faslane naval base in Scotland.

"I've brought sturdy boots and my waterproofs, though. I'm sure I'll need them after the summer we've had."

Even the most ardent climate change protester, it seems, is forever at the mercy of British weather.