Japan is celebrating a groundbreaking science experiment in the Arctic permafrost that may eventually reshape the country's fragile economy and Tokyo's relationships with the outside world.

For an unprecedented six straight days, a state-backed drilling company has managed to extract industrial quantities of natural gas from underground sources of methane hydrate - a form of gas-rich ice once thought to exist only on the moons of Saturn.

In fact, the seabeds around the Japanese coast turn out to conceal massive deposits of the elusive sorbet-like compound in their depths, and a country that has long assumed it had virtually no fossil fuels could now be sitting on energy reserves containing 100 years' fuel. Critically for Japan, which imports 99.7 per cent of the oil, gas and coal needed to run its vast economy, the lumps of energy-filled ice offer the tantalising promise of a little energy independence.

Environmentalists, though, are horrified by the idea of releasing huge quantities of methane from under the seabeds. Although methane is a cleaner-burning fossil fuel than coal or oil, the as yet untapped methane hydrates represent “captured” greenhouse gasses that some believe should remain locked under the sea. The mining of methane ice could also wreak havoc on marine ecosystems.

Japan is growing ever-more desperate to secure its energy, as once-reliable suppliers - such as Indonesia and Australia - have begun either to cut back exports of natural gas and coal or charge crippling prices.

Its direct interests in vital global energy projects, such as oil drilling in Sakhalin and Iran, have also been whittled away by politics and diplomatic rivalries.

The potential of methane hydrates as a source of natural gas has been known scientifically for some time, though how much was lurking off the Japanese coast has been confirmed only in the past couple of years. Methane hydrates are believed to collect along geological fault lines, and Japan sits atop a nexus of three of the world's largest.

In 2007 the Ministry of Economy, Trade and Industry declared that there were more than 1.1 trillion cubic metres (39 trillion cubic feet) of methane hydrates off the eastern coast - equivalent to 14 years of natural gas use by Japan at current rates. Academic studies suggest total Japanese deposits of 7.4 trillion cubic metres.

Realising how valuable the technology of unlocking the methane hyrdrates could be, Japan has invested frenziedly in the science of exploiting them. The Japan Oil, Gas and Metals National Corporation (Jogmec) has, for more than a year, been experimenting with the methane hydrate reserves under the tundra of northwestern Canada. Its six-day continuous extraction of methane from a deposit more than a kilometre below the Earth's surface has been hailed as the breakthrough Japan had been waiting for: undersea experiments in Japanese waters are to begin early next year. Commercial production, a Jogmec spokesman told The Times, would begin within the decade.

The Japanese Government is so excited at the prospect of even modest relief from its energy problems that it has drawn up a basic policy for ocean-related extractions. It may also licence the technology to allow China, South Korea and other nations thought to have large methane ice deposits off their coasts to unleash the potential of the flammable sorbet.

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