Britain is poised to get much bigger. South Africa, Russia, France, Brazil, Australia and Ireland are hoping to expand too. In fact, 45 countries with coastlines qualify for potential "extended underwater territory" rights under the new UN Law of the Sea Convention. This new law, due to come into force in a few years time, has provoked a scramble for underwater land almost as fierce as the one for Africa in the 19th century when European countries divided up the continent between them.

The 21st century land rush is likely to be the last big shift in land ownership in centuries and reflects the necessity to claim new seams of the Earth's resources.

In total, as much as 2.7m square miles - an area similar in size to Australia - is believed to be at stake. It includes the Arctic where Russia recently claimed land below the north pole, new islands off India which have emerged from the sea, and Pacific ocean islands claimed by Australia. But to claim the new underwater land, countries must be able to show that it is an extension of their own topography, and not just a gratuitous land grab. All claims must be staked by spring 2009, which is why there is a rush to gather scientific evidence to support submissions.

Significance
The new UN law means that specks in the oceans, such as Ascension Island and the Falklands have acquired new diplomatic significance. With each landfall comes the possibility of a 350 mile circle of hydrocarbon and mineral potential.

The lure of the Earth's final frontiers is the possibility of oil, gas and minerals deposits. Shrinking resources and growing energy needs mean any new territory is at a premium, particularly as new technologies are changing the face of exploration and mineral recovery. The idea of drilling for diamonds off South Africa, or for oil five miles deep off Australia seemed impossible only a decade ago. Today they are real possibilities.

There is also growing awareness of "oil peak", the point when global demand for oil will outstrip supply. This week Lord Oxburgh, former chairman of Shell, told a conference in Ireland the tipping point could come within 20 years as production levelled and new deposits became harder to find. "The world may be sleepwalking into a problem which is actually going to be very serious and it may be too late to do anything about it by the time we are fully aware," he said.

Britain has long been aware of the potential of three of its territorial gains. Its companies have seismically tested the seabed off Ascension Island, Rockall and the Falklands but no wells have been drilled to date and no economically significant hydrocarbon discoveries have been made.

However, geologists are optimistic that a large area of seabed running from the Bay of Biscay past the west coast of Ireland and into the Atlantic could be hiding a massive new oilfield.

Rockall, the 25-metre (80ft) lump of granite which is claimed by Iceland, Ireland, Norway and Britain, is expected to be of enormous significance. When British marines raised the flag there in 1957, they had no inkling there was anything but fish around. At the time it was described as the last land grab of the British empire. Today environmentalists argue it was the first of British eco-colonialism.

Drilling
The depths of the ocean in many of the new lands being claimed are beyond the current technical limit for successful sub-sea prospecting. But exploratory oil drilling is going on in the Gulf of Mexico three miles beneath the surface.

As well as oil, gas and mineral deposits, some scientists are excited by the potential of methane hydrates, a form of water that contains a large quantity of methane gas and remains solid under high pressures in the deep seas. Large deposits have already been found in the Gulf of Mexico and the Caspian Sea. Environmentalists fear exploitation of methane hydrates could trigger a runaway reaction that could alter the climate and release vast quantities of greenhouse gases.

Roaring rock
· Rockall is the summit of the eroded core of an extinct volcano.

· The rock is about 25 metres wide at its base and rises sheer to a height of approximately 22 metres (72 ft) although it is regularly washed over by large storm waves, particularly in winter. Its permanent inhabitants are only periwinkles and other molluscs.

· The earliest recorded landing on the island was on July 8 1810 when a Royal Navy officer called Basil Hall led a small landing party from the frigate HMS Endymion to the summit.

· It has been suggested that Rockall derives from the Scottish Gaelic Sgeir Rocail, which is often translated as roaring rock, although rocail can also be translated as tearing or ripping.

· The first literary reference to the isle, where it is called Rockol, is found in Martin Martin's A Description of the Western Isles of Scotland, published in 1716

· The island in the north Atlantic is 187 miles west of the uninhabited island of Soay, St Kilda, Scotland and 263 miles north-west of Donegal in the Republic of Ireland.

(By John Vidal, The Guardian, 22/09/2007)