Spelling out his vision of "Britishness", he said that "blood alone" did not define national identity and modern Britain was shaped by a "rich mix of all different ethnic and religious origins over the centuries".

His speech was attacked by Conservative leader William Hague as the rival leaders tried to appeal to the patriotic voter.

"Qualities of creativity built on tolerance, openness and adaptability, work and self improvement, strong communities and families and fair play, rights and responsibilities and an outward looking approach to the world that all flow from our unique island geography and history.

"If these values are what makes us British ... then devolution is a necessary part of keeping Britain together."

Mayors with power

Turning to devolution within England, Mr Blair defended the government's decision to press ahead with city mayors saying they "made sense".

He added: "City mayors with real power have their place, hereditary peers in the House of Lords don't, and a constructive engaged attitude to Europe reflects the best of British values of openness and leadership in the world."

Mr Blair also stressed his belief in the Union saying: "The United Kingdom is stronger together than apart."

He attacked the Tories' policy of English votes for English laws, saying it was important that all MPs voted together in the Commons with no "second class citizens".

Turning to Europe, Mr Blair said: "Standing up for Britain does not mean being anti-Europe. It is not pro-British to be anti-Europe."

Mr Blair's appeal to a united Britain still coming to terms with devolved government provoked criticism from opponents.

Mr Hague said the prime minister's attempts to claim "Britishness" for Labour were "laughable".

He added that Mr Blair "conspires to sell out the British national interest by scheming to scrap the pound and by refusing to stand firm against the drift towards a European superstate".

Liberal Democrat leader Charles Kennedy also took Labour to task over its handling of the constitution.

But he had some praise for devolution and attacked Mr Hague saying the Tory leader was taking his party down a "narrow cul-de-sac of nationalism".

Joining the debate, John Adams of the Campaign for the English Regions said: "The union is stronger for devolving power to Scotland and Wales.

"But far too much power is still concentrated in Whitehall and Westminster and the English regions are being left behind."