The Foreign Office reportedly asked politicians and diplomats to drop the phrase last year. But Mr Benn's open criticism surprised many observers, and critics suggested he might be attempting to woo grassroots Labour activists in his bid for the party's deputy leadership - an accusation he later described as "unworthy".

"In the UK, we do not use the phrase 'war on terror' because we can't win by military means alone, and because this isn't us against one organised enemy with a clear identity and a coherent set of objectives," he told a meeting in New York organised by the Centre on International Cooperation.

"It is the vast majority of the people in the world - of all nationalities and faiths - against a small number of loose, shifting and disparate groups who have relatively little in common apart from their identification with others who share their distorted view of the world and their idea of being part of something bigger. What these groups want is to force their individual and narrow values on others without dialogue, without debate, through violence. And by letting them feel part of something bigger, we give them strength."

He said "hard power" was not enough: "It can certainly win the battle, but without soft power we cannot win the war that will deliver better governance, sustainable peace and lasting prosperity."

Tony Blair's spokesman said he was unsure when the prime minister had last used the term, adding: "We all use our own phraseology." He said Mr Blair believed that "in fighting terrorism you should both use military means where necessary but also political means as well".

Michael Moore, the Liberal Democrat foreign affairs spokesman, said: "The so-called 'war on terror' has always been a flawed concept. Many will be cynical about Hilary Benn waiting until he is running for deputy leader of the Labour party before making these comments."

US sources played down Mr Benn's criticism. David Johnson, deputy chief of mission at the US embassy, told Radio 4's PM programme: "Mr Benn makes an important point we not only do not disagree on, but embrace: the solution will come not just with military force but development and working with other governments."