Speaking to left-wing leaders from 139 countries at the Socialist International conference in Paris, Mr Blair pursued his agenda of radical modernisation which he set out at Labour's annual conference in September.

Mr Blair said those from left and right who opposed change had to be challenged.

He called on left-wing leaders to be "modernisers with a purpose - to create a society of fairness and enterprise for all".

The speech is the latest instalment in the prime minister's Third Way ideology, in which he seeks to chart the middle ground between market forces and traditional state intervention.

Ditching dogma

The prime minister's audience included both the French Prime Minister, Lionel Jospin, and German Chancellor Gerhard Schroeder, who had already launched German version of the Third Way - Die Neue Mitte.

Gerhard Schroeder: Another advocate of the Third Way

Mr Blair added: "The debate today is no longer about whether we modernise, but how and how fast.

"My case is straightforward. The left and centre-left has to stay true to its values but rediscover fundamental radicalism in applying those values to the modern world and jettison outdated doctrine and dogma that stands in our way.

"In history the left always wins when it is not just about justice but about the future too.

"We must take on the forces of conservatism, left and right, who resist change - whether it is the right who believe the knowledge economy is just a passing fad, or those parts of the left happy defending the status quo, promoting tax and spend or yielding up the territory of law and order to the right."

Mr Blair told his audience that Tuesday's pre-Budget statement by the Chancellor Gordon Brown, and the forthcoming Queen's Speech, would set concrete examples of the Third Way.

Both would set out the next steps in the modernisation of the UK and will focus on the enterprise and fairness, he said.

'Liberating potential'

The prime minister added that the Third Way, "is about modernising social democracy in a way that liberates the potential of every individual, not the few represented by the right."

He told delegates that "human capital" rather than land or machinery was vital for success.

Mr Blair said: "Waste the talent of any one person, we make the nation poorer. Unemployment is not just morally wrong, it is economically inefficient."

Also at the three-day congress will be Italian Premier Massimo D'Alema and Portuguese Prime Minister Antonio Guterres.

Lionel Jospin: More orthodox approach

Other delegates include Israeli Prime Minister Ehud Barak; Palestinian leader Yasser Arafat; South Africa's Deputy President Jacob Zuma; Moroccan Prime Minister Abderrahmane Youssoufi; and Argentine President-elect Fernando de la Rua.

Before his speech Mr Blair played down the political differences between the British and French governments.

In a column in the French newspaper Le Journal de Dimanche, he said: "Certain people want to see incompatibilities in the beliefs of the centre-left in France and Britain ... they are wrong.