Native Americans are to join the Climate Camp protests in the City of London this week in an attempt to draw attention to corporate Britain's "criminal" involvement in the tar sands of Canada.

A worker walks between huge trucks in Fort McMurray, Alberta. The oil sands extraction process requires top soil to be removed, is highly energy-intensive and releases huge amounts of carbon dioxide. (Photograph: Orjan F. Ellingvag/Dagens Naringsliv/Corbis) Five representatives from the Cree First Nations are coming to co-ordinate their campaign against key players in the carbon-heavy energy sector with British environmentalists.

Eriel Tchekwie Deranger, from Fort Chipewyan, a centre of Alberta's tar sands schemes, said: "British companies such as BP and Royal Bank of Scotland in partnership with dozens of other companies are driving this project, which is having such devastating effects on our environment and communities.

"It is destroying the ancient boreal forest, spreading open-pit mining across our territories, contaminating our food and water with toxins, disrupting local wildlife and threatening our way of life," she said.

It showed British companies were complicit in "the biggest environmental crime on the planet" and yet very few people in Britain even knew it was happening, said Deranger. She was speaking ahead of an annual Climate Camp that will be held for one week somewhere in Greater London from this Thursday.

The exact site of the camp has not been revealed as green organisers are worried that the police might move to thwart their plans if they are notified in advance.

BP and Shell are two of the major oil companies extracting oil from the tar sands. The thick and sticky oil can only be removed from the sands by using a lot of water and power as well as producing far heavier CO₂ emissions.

RBS, now partly owned by the British government after its financial rescue, is also a target of environmentalists and aboriginals because it is seen as a major funder of such schemes.

The Climate Camp concept started with a protest outside the Drax coal-fired power station in North Yorkshire and was followed up by similar protests at Heathrow - against the proposed third runway - and Kingsnorth in Kent, where E.ON wants to construct a new coal-fired power station.

There was also a Climate Camp in April at Bishopsgate inside the City of London, which became linked with bad policing after a bystander died following a clash with a constable.

The tar sands are seen by many as a particularly dangerous project providing enough carbon to be released in total to tip the world into unstoppable climate change. Shell was the first major European oil company to invest in the Canadian-based operations but BP followed under its chief executive, Tony Hayward.

The oil companies both dispute the amount of pollution caused by tar sands and insist they must be exploited if the world is not going to run out of oil.

But George Poitras, a former chief of the Mikisew Cree First Nation, said the so-called heavy oil schemes were violating treaty rights and putting the lives of locals at risk. He said: "We are seeing a terrifyingly high rate of cancer in Fort Chipewyan, where I live. We are convinced these cancers are linked to the tar sands development on our doorstep."