Remember the Iranian hostage crisis between 1979 and 1981? This, surely, was the lowest point in American foreign policy since 1945. The botched attempt to rescue the hostages defined the failure of the Carter presidency, just as their release indicated that the Reagan era would be different.

Well, now we have a new Iranian hostage crisis. By “we” I mean in the first instance the British. Last Friday, eight royal navy sailors and seven royal marines were taken prisoner by Iranian Revolutionary Guards while carrying out a routine inspection of a cargo ship, on the false pretext that they had entered Iranian waters illegally. This was unmistakably an act of war.

Since then, the Iranians have refused to give any information about the whereabouts of the captives, let alone consular access. All we know is that they are being interrogated and accused of espionage. There have been hints that a show trial is being prepared. So-called students have already held a mock trial of the hostages that ended in shouts of “death to Britain.”

The Foreign Office reflex in these situations is to appease. It did so in a similar incident that occurred in 2004, when eight marines were captured. The Foreign Office prides itself on the fact that the marines were soon released. It omits to mention that the marines were physically abused by their guards and humiliated by being forced to grovel on Iranian television. One of their boats is on display in Tehran as a trophy.

The feeble British response three years ago will have emboldened the Iranians to go further this time. They know how these stories will be depicted in the Western press. The commander of HMS Cornwall, the hostages’ parent warship, had a BBC television crew on board at the time. What could the poor man do?

The fact that one of the sailors is a woman, Leading Seaman Faye Turney, adds greatly to the hostages’ propaganda value, because public opinion is assumed to have no stomach for any policy that risks worsening the plight of this young mother. The Iranians have no scruples about exploiting the presence of women in Western armed forces. In view of their record, the foreign secretary, Margaret Beckett, should not have accepted the assurances of her Iranian counterpart that the 15 hostages are “fit and well” and that “all ethics have been observed” in the treatment of Ms. Turney.

Tony Blair published evidence this week to prove that the captured Britons were not in Iranian waters. True, but Iran took British hostages because they could — and with impunity, too. Mr. Blair said that it was time that “we” began to “ratchet up” the pressure on Iran. So the question is: Does the “we” include you?

So far, America has offered diplomatic support, but American public opinion has taken little notice. True, American warships have just begun a big naval exercise in the Gulf. But it will take more than saber rattling to face down a government that has defied the West for decades.

Privately, the royal navy is fuming. An American officer in the same task force was not impressed: “Our reaction was: ‘Why didn’t your guys defend themselves?'” The answer is: British rules of engagement. The marines and sailors were probably under orders not to shoot. Nor could HMS Cornwall use her missiles to destroy the Iranian gunboats, for fear of precipitating a crisis.

The crisis, however, is happening anyway. In return for the British hostages, the Iranians may demand the release of five Revolutionary Guards captured inside Iraq. America would rightly reject such a deal out of hand. There is no equivalence between British sailors carrying out a U.N. mandate and Iranian agents helping Shiite militias to murder American or British troops.

The British should be pressing for a Security Council resolution, setting a date for the release of the hostages and authorizing the use of force if necessary. British diplomats are not safe in President Ahmadinejad’s Iran. They should be packing their bags.

With Congress breathing down his neck, President Bush does not want a showdown with Iran until he is ready for one — not now and not over hostages who aren’t even American. So if Mr. Blair wants Mr. Bush’s support, he needs to take a tougher lead himself. Americans admire courage, and Mr. Blair has already proved that he is a brave man. It would help if Mr. Blair made clear that the rules of engagement will change so that British forces are no longer obliged to surrender without a fight.

When Hezbollah crossed the Lebanese border to take hostages in Israel last summer, the Israelis resisted fiercely and several of the unit soldiers were killed. Israel treated the incident as the act of war that it was, and Israeli forces received full American support to go after Hezbollah. The former U.N. ambassador, John Bolton, told a shocked BBC interviewer last week: “I’m damn proud of what we did.”

If the British want their hostages to get sympathy in America, they need to start behaving less like Europeans and more like Israelis. There is no point in gunboat diplomacy if you aren’t prepared to use your guns.