A GIANT coral "barrier reef' running parallel to Britain's northern coasts has been found deep under the Atlantic in areas previously considered among the coldest and most barren on earth.

The reef, thought to be thousands of years old, was built by coral polyps - tiny animals similar to those that build tropical reefs-which have adapted to life at enormous depths.

It was discovered by researchers attempting to assess the environmental damage that may be caused by companies granted licences to drill for oil in the sea northwest of Scotland.

Preliminary surveys suggest the reef covers hundreds of square miles of seabed. Some scientists believe it could emerge as the most important eco-system in the north Atlantic.

This week, the Natural Environment Research Council will announce a £180,000 programme to map the reef and study its biology.

Graham Shimmield, director of the Scottish Association for Marine Science, whose surveys have indicated the size of the reef, has been asked to carry out the work.

"Tropical reefs are usually long and narrow, but this is spread across the seabed at depths between 1,000 and 2,500 feet. It covers a far wider area than anyone ever realised," he said last week.

The polyp responsible for the reef, Lophelia pertusa, is thought to grow at less than a centimetre a year, suggesting that parts of the reef could be thousands of years old. Tomorrow, however, a conference of marine biologists at London University will hear that as well as being one of Britain's newest and most important scientific discoveries, the reef is one of the most endangered.

It lies in an area dubbed the "Atlantic Frontier", which has oil reserves estimated at more than 1.2 billion tons-so huge that it could become more productive than the North Sea. Last April the government issued exploration licences to some of the world's biggest oil companies. They are already scouring the area.

Marine biologists believe the reef could be vulnerable to such disturbances. In the tropics thousands of miles of reef have been destroyed by excessive fishing and pollution.

Dr Sian Pullen, head of marine conservation at the World Wide Fund for Nature, said the government had issued the licences without any real idea of possible damage. "There should have been a full assessment of just what is down there before the licences were handed out," she said.

Research indicates that the reef is home to at least 300 fish species.