Not to be outdone by President Sarkozy’s amorous overture to President Bush in Washington, Prime Minister Brown of Britain has used the first major foreign policy speech of his premiership to insist that Britain is America’s closest ally.

After decades of Anglo-French rivalry, in which France has vehemently deplored the global influence America and Britain have attained and what every president of France since Charles de Gaulle has described as “Anglo-Saxon culture,” Mr. Sarkozy claimed during his visit to Washington last week that France, not Britain, is now America’s best friend and partner.

Mr. Brown, who has been portrayed on both sides of the Atlantic as having distanced himself from America to avoid the charge against his predecessor, Tony Blair, that he was Mr. Bush’s “poodle,” fought back last night, claiming in a speech at a banquet thrown by the lord mayor of the city of London that the French president’s bid to usurp Britain’s traditional place alongside America would not succeed.

“It is no secret that I am a lifelong admirer of America,” Mr. Brown said. And, in a thinly veiled reference to France’s traditional dislike of America and its culture, he added, “I have no truck with anti-Americanism in Britain or elsewhere in Europe, and I believe that our ties with America — founded on values we share — constitute our most important bilateral relationship.”

He welcomed France’s late conversion to the American cause and a similar newfound affection for America expressed by Chancellor Merkel of Germany in her visit to Mr. Bush’s ranch in Crawford, Texas, over the weekend.

“It is good for Britain, Europe and the wider world that today France and Germany and the E.U. are building stronger relationships with America,” Mr. Brown said. But he emphasized that it is with America, not Europe, that Britain maintains its “most important” relationship.

“The strength of our relationship with America is incredibly important to the future of the world,” Mr. Brown said in an accompanying television interview with Sky News. “If we’re going to rebuild the international institutions as I think we should be doing, to meet the challenges of the next stage, then we want to work with America to enable us to do so.”

Mr. Brown’s comments will come as a slap to a former U.N. official, Mark Malloch-Brown, now a British foreign minister, who declared shortly after his appointment that since Mr. Brown’s arrival in Downing Street, America and Britain were no longer “joined at the hip.”

The maverick Lord Malloch-Brown, who has angered many members of the Bush administration with anti-American statements, was instantly reprimanded by the British foreign secretary, David Miliband, and has since found himself obliged to apologize for suggesting that Britain should start negotiating with the Islamist terrorist groups Hezbollah and Hamas.

Along with a furor in the British press over the free living accommodation provided for him by the British government, Lord Malloch-Brown’s days in Mr. Brown’s government appear to be numbered.

Mr. Brown also used his Mansion House speech to express his backing for America’s robust opposition to Iran’s nuclear weapons ambitions, saying the mullahs in Tehran must choose between “confrontation” and a “transformed relationship with the world.”

“Iran should be in no doubt about our seriousness of purpose,” he said. “We will lead in seeking tougher sanctions both at the U.N. and in the European Union, including on oil and gas investment and the financial sector,” he said, unless the Tehran regime conforms to international demands to halt uranium enrichment and allow inspectors to inspect nuclear facilities.

The prime minister was at pains to point out that he would not be soft on those countries that threaten peace.

“My approach is hard-headed internationalism,” he said. “Internationalist because global challenges need global solutions and nations must cooperate across borders, often with hard-headed intervention, to give expression to our shared interests and shared values. And hard-headed because we will not shirk from the difficult long-term decisions and because only through reform of our international rules and institutions will we achieve concrete, on-the-ground results.”

Following his own advice, Mr. Brown demanded that martial law in Pakistan be ended without delay and democracy be reinstated. “We call on President Musharraf of Pakistan to restore the Constitution and implement the necessary conditions to guarantee free and fair elections on schedule in January,” he said.

He also proposed broadening the membership of organizations like the United Nations, the Group of Eight, the International Monetary Fund, and the World Bank to make the bodies more purposeful. The U.N. Security Council should be changed to make it “more representative, more credible, and more effective,” he said.

“We cannot any longer escape the consequences of our interdependence,” he said. “The old distinction between ‘over there’ and ‘over here’ does not make sense of this interdependent world. There is no longer an ‘over there’ of terrorism, failed states, poverty, forced migration, and environmental degradation, and an ‘over here’ that is insulated or immune.”

In the light of the conflicts in Iraq, Afghanistan, and elsewhere, where dictatorial regimes degraded a nation’s institutions, Mr. Brown advocated the forming of an international “standby civilian force,” including police and judges, to “rebuild civic societies.”