It came as diplomats gave warning that British attempts to solve the crisis prompted by Tehran’s resumption of its nuclear programme last week were doomed to failure.

Bush raised the temperature by giving an interview to Israeli television from his ranch in Crawford, Texas. Asked if he would consider force, he replied: “All options are on the table.” He added: “The use of force is the last option for any president and you know we’ve used force in the recent past to secure our country.”

The Foreign Office reacted swiftly. “Our position is clear and has been made very, very clear by the foreign secretary,” a spokesman said. “We do not think there are any circumstances where military action would be justified against Iran. It does not form part of British foreign policy.”

So soon after the invasion of Iraq, which has led to so much political turmoil for Tony Blair’s administration, Straw is anxious not to be seen trying to talk up any future forays. But some rightwingers in Washington have criticised Straw’s position, saying that every time the foreign secretary rules out any remote chance of military action the Iranians know there is no need to compromise.

Bush’s veiled remarks came as Foreign Office negotiators launched a new round of shuttle diplomacy to try to persuade Tehran to reverse last week’s decision to resume its enriching of uranium — seen by Washington and the European Union as a smokescreen for a secret nuclear weapons programme.

A spokesman said Britain’s negotiators had “worked their socks off” to convince a meeting in Vienna of the board of the International Atomic Energy Agency (IAEA) to call on Iran to freeze activity at its Isfahan and Natanz plants.

Britain has made it clear that if Iran has not backed down by September 3, when Mohamed ElBaradei, the IAEA’s secretary-general, is to report on the country’s nuclear programme, it will push for Tehran to be taken to the United Nations security council. Officials in Vienna warned, however, that any attempt to impose sanctions on Iran would be likely to be vetoed by Russia and China.

“Iran has all the cards,” said one official close to the talks. “It’s going to be embarrassing for the Brits.”

Russia has a civilian nuclear contract with Iran worth £500m while China is increasingly reliant on Iranian oil and gas. Last October Sinopec, the Chinese state oil company, signed a £39 billion deal giving it a 51% stake in Yadavaran, Iran’s largest onshore oilfield.

For two years Britain, France and Germany have represented the EU in negotiations with Iran, which insists that it has a legal right to make its own nuclear fuel. The issue has become a rallying call in Iran, and Mahmoud Ahmadinejad, the new president, is thought unlikely to make any concessions.

Cyrus Nasseri, Iran’s chief negotiator, dismissed EU sweeteners as “lollipops” and denounced the IAEA resolution.

Last week scientists at Isfahan broke IAEA seals that had mothballed the plant and began converting uranium “yellowcake” ore into uranium hexafluoride gas, breaking an agreement made with the EU.

Hawks in the Bush administration have been less vocal in their calls for military intervention against Iran recently, and the president’s remarks are said to belie a lack of appetite for another all-out confrontation in the Middle East.

“What you’ve got to remember is everything Iran could do for Bush,” said one diplomat. “They could make his Middle Eastern dreams come true: think of their influence in Iraq, in Lebanon, in Palestine. Think of their influence on oil prices.”

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