LONDON -- What did the Russians hope to achieve? Their threat two weeks ago, now happily averted, to cut off natural gas supplies to Ukraine unless it immediately paid four times the current contract price was bound from the start to backfire.

For one thing, it was a threat that could not be carried out. Ninety percent of the gas that Russia supplies to Western Europe under contract (which is about a quarter of Western Europe's daily consumption) passes through pipelines across Ukrainian territory.

All the Ukrainians had to do, if Russia cut supplies, was turn a couple of valves and divert gas intended for the West to their own consumers, claiming that it was theirs by right.

The explanation can only be that the threat had nothing to do with commercial factors and everything to do with the desire of Russian policymakers to punish Ukraine for turning more to the West under its new president, Viktor Yushchenko. If so, it was a remarkably ill-thought-out move, since the only result in the longer term can be to weaken trust in Russia as a reliable energy supplier.

Prolonged and assured trust is absolutely essential in the delivery of energy supplies, and nowhere more so than with piped gas. This is because once the pipeline is built and laid there must be assurance for every hour and every day, for years ahead, that gas from a specific reservoir will flow. This is not only to justify the cost of laying the pipeline in the first place but because, in the case of natural gas, the pipeline becomes extremely dangerous if it is not kept filled (although the pressure can vary somewhat).

Continental Europe decided several decades ago, even before the demise of the Soviet Union, that it could rely heavily on Russian gas, piped from Siberia, as a key component in its energy-supply mix. When the contracts were first signed, one or two voices were raised, including that of British Prime Minister Margaret Thatcher, arguing that this was a dangerous move.

But such doubts were dismissed on the grounds that even in the Communist days the Russians were scrupulous adherents to commercial bargains. In the years that followed, and especially with Russia's moves to turn capitalist, these doubts were given even less weight. The gas, said optimists, would always come through.

Meanwhile, gas consumption in Western Europe soared as privatization of electricity generators led to the replacement of massive old oil-fired and coal-fired generating stations with smaller and highly profitable gas-turbine generating plants, which could be built much more quickly and thus pay back the initial investment to increasingly happy shareholders.

Britain, too, shared in this gas demand bonanza, raising its proportion of electricity supplied from burning gas from 1 or 2 percent in the early 1980s to around 30 percent today -- in addition to the very widespread use of gas for domestic cooking and heating that now involves some two-thirds of all households in the country. Gas usage has been further encouraged by the argument that although it is a finite fossil fuel it emits far less carbon dioxide when burned than does oil or coal and is, therefore, environmentally preferable.

The North Sea "natural gas" discoveries in the 1950s and '60s on Britain's continental shelf kept Britain well supplied until very recently. These have gradually run down, though, and now the British buy their gas from a variety of sources, notably the Norwegians but also from the French, Germans and Dutch.

This in effect has re-integrated British gas supplies with the giant Continental grid, which relies so heavily on the Russians. So, despite the Thatcher warning of years ago, Britain has ended up in almost the same position as its neighbors, relying, albeit indirectly, on Russian common sense and trust to keep the pipelines going westward full at all times.

Some experts, while recognizing the dangers of relying too much on one source, whether for political or security reasons, have argued that all will be well because Europe, Britain included, can freeze gas and transport it as liquid natural gas or LNG, which can be shipped to domestic terminals from suppliers such as Algeria and Qatar in the Persian Gulf.

In the recent cold weather in Europe, and with more and more oil users turning to gas as the oil price climbed, this seemed the best new avenue for regular supplies -- an avenue that Japan has relied on for many years.

But imagine the dismay recently when huge LNG-carrying carriers, bound from the Gulf for northern Europe, were suddenly diverted to the United States East Coast by more attractive price offers. The full consignment of LNG expected at one major British terminal, specially constructed for the purpose, never arrived.

The implication is clear: Just as there is now a faint question mark over the reliability of Russian gas supplies, so too is there over the frozen gas alternative. Either future contracts will have to be made a lot tighter, and less dependent on short-term market price fluctuations, or the British will need to look elsewhere for safe gas supplies.

Luckily, another alternative exists on the doorstep. The Norwegians have been finding more and more gas, in huge volumes, on their side of the North Sea, and are very happy to sell it direct into the British system on the basis of very long-term contracts. All that is needed is a good system of pipelines to convey the gas from these great new North Sea fields into the British grid. These are now hurriedly being completed.

The British can then heave a small sigh of relief and leave the rest of Western and Central Europe to get as much reassurance as they can from the Russians. The Russia-Ukraine incident makes one thing notably clearer than before: There is a lot of politics in gas.