When in a hole, first stop digging. The Pithy piece of political advice coined by Denis Healey has been revived by Greenpeace to encapsulate the rationale behind its campaign against the search for oil in the North Atlantic, writes Christopher Cabas, Environment Correspondent.

Put simply, the environmentalists argue that since burning all the oil and gas the world already has in reserve would cause catastrophic climate change, it is suicidal to spend billions of pounds in looking for more.

The link between fossil fuels and global warming, accepted by the Intergovernmental Panel on Climate Change, is still disputed some oil companies but even Heinz Rothermund, managing director of Shell UK, admitted the Atlantic Frontier exploration presented "a dilemma".

Threats to the area's fragile habitat and the variety of sea life it supports is another major plank of Greenpeace's campaign - its first high-profile media venture in Britain since the battle of Brent Spar in 1995.

More than 20 species of whale use the waters west of Shetland as a migration route between the Arctic and Southern Atlantic oceans, a "whale motorway" which environmentaiists claim will be severely disrupted by seismic exploration.

Cold-water coral grows of the slopes of the continental shelf and supports 800 species of marine organism, a biodiversity as rich as a tropical rainforest. It is sensitive to 'disturbance and has a slow recovery rate.

In addition, the hostile waters contain thousands of species of sea life including 200 types of fish and, in the vast depths of the Rockall Trough, many exotic animais yet to be studied by science.

But it is the significance of the frontier as a sign that the rush for oil continues unabated which has Greenpeace particularly exercised.

"Science shows the climate cannot survive the burning of the oil we've already got," said campaign director Chris Rose. "It is an insane and hypocritical policy to look for more. Greenpeace disputes the moral and political right of the UK to develop this ocean for more oil."

In fact, Greenpeace disputes the right of any nation to look for more oil anywhere in the world, and says there are at least 15 locations where nations are competing for drilling rights and there is a real danger of armed international conflict. The time has come, it says, to agree a policy of non-development of the oceans similar to that employed in Antartica - a "global commons" of the sea should be declared and the first outpost should be in the North Atlantic.

Not surplisingly, the oil exploration industry is scathing of what it regards as sensationalism and economic naiveté. Oil and gas production in UK waters supports 330,000 jobs, accounts for ahnost 20 per cent of investment in the UK production industry and has paid about £140,000 million to the treasury.

James May, director General of the UK offshore Operators Association, said: "Whatever Greenpeace might believe should be the case in the future, life today and the expectations of consumers with regard to living standards, comfort and mobility, depend on the availability of adequate resources of fossil fuels."

The Rockall occupation marks the return of Greenpeace to the British media spotlight, two years since its somewhat Pyrrhic victory over the Brent Spar.

Although it forced Shell into abandoning plans to dump the platform at sea, it was subsequently found to have exagerated the toxic content of the structure. It also faced a backlash from the media which was criticised for having unquestioningly accepted the Greenpeace argument.

ln the meantime, a new breed of environmental campaigner has emerged, namely Swampy and every other motorway protester prepared to live in tree houses or down tunnels.

Is this an attempt by the old hands to reclaim their rightful place as the one true green conscience of the nation?

"It would be nice to think so, but I honestly believe this is Greenpeace just doing what they do best," said Richard North, environmental commentator and one of the organisation's most trenchant critics. "It is a campaign with poetic simplicity - wrong, but stylish in a way only they can achieve."

Active support for Greenpeace UK remains high, although a change in the way it records membership has given the impression of a definite dip, and its annusl income of £7 million still far outstrips any other environmental body.

"Swampy and Co. will never be able to match the power of Greenpeace," said Mr North.

"They are past-masters at negatative advertising, which is not surprising because they can afford to buy it from the same people who do the opposite for big business."