Britain's friendship with the United States is "the most important relationship in world politics", according to Iain Duncan Smith.

But the Tory leader stressed his fear, at an international gathering of centre-right leaders in Washington DC, of "a growing level of anti-Americanism", especially in Europe.

The most important relationship in world politics is the link between London and Washington

Iain Duncan Smith

Mr Duncan Smith told the International Democratic Union on Monday that a progressive Conservative agenda was about "putting people before systems" and was the difference between "promises and delivery".

He also claimed that centre-left parties were unable to offer effective leadership in tackling issues that undermine society.

Mr Duncan Smith, who was being welcomed with a dinner hosted by President George W Bush, said: "The most important relationship in world politics is the link between London and Washington.

Pressure on Europe

"If Britain and the USA are together in areas of foreign policy, then I think the chances for peace and security in the world are very great indeed," he told a group of reporters.

But he continued: "The most worrying feature at the moment in politics generally is the growing level of anti-Americanism, which is particularly strong, I think, in continental Europe but is there strongly in the left in politics in the UK."

The Tory leader argued that European leaders should do something to counter this trend.

"The idea of creating some alternative to the USA as a competitor in world politics is a very negative way of looking at life," he said.

"The reality is that when we work together we can do real things."

Bush tribute

In a speech to the IDU, which is being chaired by Tory former leader William Hague, Mr Duncan Smith insisted that the challenges ahead were "not just about winning the war against terrorism".

He took a swipe at UK Prime Minister Tony Blair's "Third Way", claiming that just as centre-left parties were "incapable of conceiving and seeing through the economic changes that enriched our nations in the 1980s, so they have been unable to offer effective leadership in tackling the issues that undermine our society today".

We do have to show how our principles will deliver solutions to the problems people face

Iain Duncan Smith

The Conservative leader paid tribute to the US president "for showing us the way".

"He has shown us that conservative parties don't have to stop being conservative to win elections, but we do have to show how our principles will deliver solutions to the problems people face."

People power

Mr Duncan Smith said the paucity of centre-left methods and the poverty of their results "are failing the most vulnerable in our society".

"Today, it falls to us to tackle the problems of crime, failing schools, family breakdown and poor healthcare.

"Now as then we will work to give people back control over their own lives, to direct power away from government to where it can be used effectively.

"If we do these things people will see the difference between a progressive Conservative agenda and the Third Way.

"It is about putting people before systems, results before theory, substance before spin. It is the difference between promises and delivery."

Mr Duncan Smith's meeting with President Bush follows ex-US president Bill Clinton's discussions with Mr Blair at the weekend about the future of the centre-left in Europe and America.