Ascension Island. Barren, 4,044 miles from Land's End, but ours says the FO

It was life as normal yesterday on Ascension Island, a barren British territorial outpost that pokes out of the Atlantic ocean 4,044 miles from Land's End.

The 1,100 residents were largely unaware that their volcanic rock was taking centre stage at the United Nations, where British diplomats were requesting sovereignty over 77,220 sq miles of submarine territory around the island.

Yesterday's slideshow presentation in New York before 21 members of the UN Commission on the Limits of the Continental Shelf (UN CLCS) laying claim to an area of the ocean floor roughly the size of the UK's entire land surface is just the first of three submissions the UK is set to make under an international law that allows states to expand their jurisdiction.

A senior Foreign Office official told the Guardian yesterday that the UK has decided to submit similar territorial claims for seabed surrounding the Hatton-Rockall area, west of Scotland, and South Georgia and the Falkland Islands in the South Atlantic.

The reason for Britain's interest? The hope of tapping into new reserves of oil, gas and minerals. At present, countries can extract resources from the seabed up to 200 nautical miles from their shoreline. But with permission from the UN commission, they can extend their jurisdiction over the seabed up to 350 miles beyond a coastline. All they have to do is show that the ocean floor is a continuation of their continental shelf.

Britain's venture is part of a global scramble for resources prompted by technological advances that make oil and gas reserves deep in the ocean more accessible. The UN commission has set a deadline of May next year for countries to submit maps and supporting scientific evidence.

Britain's claims will anger diplomats in Denmark and Iceland, who have overlapping claims to the mineral-rich Hatton-Rockall area, and Argentina and Chile, which contest sovereignty over the seabed around the Falkland Islands.

The decision follows a breakdown in negotiations between Danish and Icelandic lawyers and their British and Irish counterparts over the underwater shelf surrounding Rockall.

The Foreign Office official, who has detailed knowledge of Britain's territorial claims, said that the UK government had invited Argentina for "technical and legal" discussions about the continental shelf around the Falkland Islands, but no talks had taken place since 2005.

Agreement between neighbouring states is required if the UN commission is to award territorial rights, meaning some claims could take several decades to resolve, he said.

"Ideally we would like to reach agreement with all the parties where there are overlapping claims. But if it is not possible to resolve a dispute, then we will be preparing a submission [to the UN CLCS] anyway, as the UK." He added: "I can confirm we will be making all three additional submissions by May 2009."

He added that Britain "reserves the right" to lodge submissions over the British Antarctic Territory, although it has no immediate plans to do so.

The Ascension Island claim means the UK has officially joined 11 other countries staking claims to submarine territory. A further 30-40 are expected to lodge claims, including some developing countries.

Although it could take up to three years for the commission to rule on Ascension Island's continental shelf, the Foreign Office is confident of success.

Speaking from his office overlooking a beach, Michael Hill, Ascension Island's administrator, said that the submission to the UN could only benefit residents. "It is clearly, having read a bit about it, a very long-term project."

Yesterday's delegation of legal and scientific experts, led by Doug Wilson, a legal adviser to the Foreign Office, and Lindsay Parson from the National Oceanography Centre, in Southampton, presented the commission with supporting geological and geophysical surveys.

"Ascension Island is going to be the only [territorial claim] that is relatively unproblematic," said Martin Pratt , director of Durham University's International Boundaries Research Unit.

"There could always be a scientific spanner in the works, but it's going to be a simple question of the commission assessing whether the areas claimed are legally part of the [island's] continental shelf."

The vast Hatton-Rockall basin, off the west coast of Scotland, believed to be rich in hydrocarbons and mineral deposits, is likely to prove more controversial.

It has been the subject of a seven-year wrangle between the UK, Ireland, Denmark and Iceland.

Shuttle diplomacy appears to have reached stalemate. Recent meetings in Reykjavik, Dublin and Southampton failed to agree maritime borders. The Danes and Icelanders are likely to stake out extensively overlapping claims.

Technological advances had raised expectations that wells could soon operate commercially, even in the storm-blasted seas around Rockall. The government is already offering exploration blocs in the area close to the outer limit of the UK's 200 mile economic zone.

The UN regulations do not, however, allow small islands that have never been inhabited to be the basis of claims for extending control over the surrounding seabed. Britain's claim on Rockall is currently based on measuring out from the island of St Kilda in the Outer Hebrides.

Rockall was Britain's last colonial land grab, annexed by a boarding party from HMS Vidal in 1955. A plaque was cemented atop the desolate rocky pillar that protrudes 63 feet above the Atlantic. The sailors sang "God Save the Queen" and gave three cheers.