This may not be a major crisis, but it's a warning of grief ahead over Iran

It is dismaying to suppose oneself fighting a war against one party, only to suffer humiliation at the hands of another. The Royal Marines and sailors who set forth on Friday to patrol the Shatt-al-Arab waterway carried loaded guns. They would have used these if necessary against Iraqi smugglers or insurgents. Instead the British were trapped by Iranian gunboats. Any attempt to defend themselves would have precipitated a disastrous clash. The outcome would have been the same, but with blood on the water. The Iranians seem to have planned this operation for days. They wanted western hostages, probably to exchange for their own people held by the Americans, and would have been untroubled by a firefight.

In international relations, a reputation for recklessness has its advantages. Iran is governed by people who seek to make mischief for the west, and are largely indifferent to its consequences. More than that, because of Iraq (almost every twist of western foreign policy is influenced by those fatal words) the British position is nowhere near as strong as it should be in haggling to get its people back.

President Ahmadinejad knows that most of the world questions the legitimacy of the western military presence in Iraq and its claimed territorial waters. Whatever angry noises are being made by Britain, in many countries this incident is regarded with indifference, or worse. Their governments and peoples believe that our forces have no business on the Shatt-al-Arab in the first place.

Here is a new manifestation of the loss of moral authority resulting from the Iraq policies of George Bush and Tony Blair. Iran is controlled by one of the most repressive regimes in the world. Its cruelties fall not merely on its opponents, but upon its entire female population. It is a proponent of international terrorism, committed to the illegal acquisition of nuclear weapons. Its president is a Holocaust denier.

Yet in dealing with Tehran, Washington and its allies must duck and weave. Iraq has drained from the international community any appetite for a showdown. Opinion polls show many people around the world are more fearful of President Bush launching strikes against Iran's nuclear facilities than of the consequences of President Ahmadinejad acquiring weapons of mass destruction.

Despite the strong line towards Iran's nuclear defiance adopted by the UN security council, now with unexpected Russian support, it is generally assumed that the country will achieve its aim of making nuclear weapons. The international effort to halt Iran's nuclear programme is a charade. Whatever sanctions are imposed, even Tehran's so-called moderates, such as Akbar Hashemi Rafsanjani, are committed to nuclear fulfilment. Washington and its allies know this. The international effort to stop the Iranians must continue, because acquiescence seems even less tolerable than unsuccessful resistance. But the outcome, probably around the end of this decade, is scarcely in doubt.

It is hard to believe that Bush and Cheney can pursue a military option, amid the deep scepticism of their service chiefs. A sustained air campaign might delay Tehran's bomb, but it is unlikely to prevent it. Only a ground invasion could achieve a decisive result, and this is a bridge too far, even for the neocons.

Thus the west is reduced to haggling with Iran, a frustrating process in the face of its leaders' institutionalised mendacity and irrationality. Ahmadinejad and his colleagues have everything to gain from a stable, peaceful Iraq next door. Instead they are fomenting the Shia insurgency, because they value the objective of embarrassing the US and its allies more than any other.

Tehran ought to be chastened by its economic predicament. Undeclared financial services sanctions, promoted by Washington, are tightening constantly. Many of the west's leading financial institutions will not deal with Iran. Its oil industry is crippled by lack of foreign investment. If America halted the trade in refined petroleum products, every Iranian would soon suffer. The country possesses facilities to process only 60% of its own fuel needs.

There is plentiful anecdotal evidence, that many ordinary Iranians are disillusioned with President Ahmadinejad, and want normal economic relations with the outside world. Frustration will be intensified by the prospect of higher fuel prices and even - fantastically, in an oil-producing country - of rationing. Yet again and again since the 1979 revolution, Iran's moderates have been thrust aside. As in Iraq, Afghanistan, Zimbabwe and other troubled societies, many of those who opposed tyranny have voted with their feet and left, to make new lives abroad. Optimists noted that Ahmadinejad's supporters fared poorly in December's local elections. There is speculation that he will lose the next presidential poll, due in 2009. Yet 2009 seems a long way from today. There is no convincing evidence that the Iranian people are anywhere near to espousing detente with the west.

The victim culture, the belief that Iran is a beleaguered nation, oppressed economically, culturally, politically and militarily by the US and its allies, is deeply rooted. It has been intensified by President Bush's pronouncements and actions over the past six years.

The European nations have always believed that engagement with Iran is the most plausible policy, for lack of any other. Belatedly, Condoleezza Rice, the US secretary of state, has joined this party. The objective is to persuade the Iranians, or anyway their least violent leaders, that in return for some moderation of their behaviour, the west will offer generous rewards. Washington's scepticism about this approach has been intensified by the seizure of the British personnel, which suggests that the Iranians are confident that intransigence is more effective than negotiation, that the west responds better to violence than to soft words.

In Tehran today it is likely that fierce exchanges are taking place between the leadership factions about what to do next with their captives. The likelihood is that, after extracting every ounce of perceived propaganda advantage from their humiliation, Ahmadinejad will release them. It would be premature to regard this episode as a major crisis, unless or until the Iranians commit themselves to trying and imprisoning the hapless servicemen. Meanwhile, it appears simply another milestone on the rock-strewn path trodden by Iran and the west for almost 30 years.

Ignore for a moment the prisoner seizure, a mere symptom of a mindset. The fundamental issues are Iran's commitments to terrorism, to the destruction of Israel, and to the acquisition of nuclear weapons. As long as these persist, relations between Washington, London and Tehran will remain glacial.

It will be a rash coalition commander in Iraq who again exposes British or American troops to Iranian arms. Iran is a tormented society, flailing and thrashing in a quest for international respect and influence. So long as its only claim to these things rests upon its capacity for violence and destruction, much more grief lies ahead for its own people and the rest of the world.

Max Hastings