Iain Duncan Smith provoked a bitter government backlash yesterday after he accused the Prime Minister of indulging in "designer diplomacy".
With Tony Blair preparing for a four-day visit to west Africa next week, the Conservative leader attacked him for "media grandstanding" on the world stage without any clear vision of the benefits for Britain.
But Labour claimed he had scored an embarrassing own goal on the day when the new leader of Afghanistan, Hamid Karzai, was visiting London.
Mr Duncan Smith told the Royal Institute for International Affairs in London: "The present Government has an approach to British foreign and security policy which is, at its very roots, misguided.
"The problem is simple and fundamental – it is that the Prime Minister seems to believe there are no limits to what Britain, acting as part of an all-embracing global coalition of the righteous, can and should do to make the world a better place." He said countries which tried to punch well above their weight jeopardised both their international standing and their own security. "An unfocused approach to foreign policy leads to, and is often devised in pursuit of, media grandstanding."
He said leaders should know what they could achieve from intervening in foreign trouble-spots, what practical means were at their disposal and whether they were best placed to broker a breakthrough.
"Without clarity on these points, the correct conclusion may be to stay at home, Mr Duncan Smith said. "So much of today's designer diplomacy demonstrates a worrying lack of realism."
The Tory leader contrasted the Prime Minister's willingness to commit British troops abroad with the shrinking size of the armed forces. "We cannot hope to do more in the world and yet spend less on it. That's called facing up to reality," he said.
His attack was denounced last night. Mr Blair, who said he was "astonished" at the remarks, retorted: "Since 11 September it has become absolutely obvious to everybody that events in one part of the world can dramatically affect events in another part of the world. I think it's not just right, but essential, Britain plays its role on the international stage."
The Labour chairman, Charles Clarke, said: "Iain Duncan Smith has come out in his true Thatcherite colours ... It's a sentiment which is out of time and utterly fails to meet this country's national interest and the serious challenges facing the modern world."
The Liberal Democrat foreign affairs spokesman, Menzies Campbell, said: "A Tory government would increasingly isolate Britain and remain locked in a quasi-imperial past."