The Eurosceptic leader of the Czech Republic, Vaclav Klaus, has signed the Lisbon treaty, finally giving effect to a much-delayed accord designed to overhaul the institutions of the European Union and give the bloc a greater say in world affairs.

The move forced the Tory leadership to concede defeat tonight over their plans to hold a referendum on the treaty with David Cameron promising to clarify his party's policy on Europe tomorrow.

William Hague, the Shadow Foreign Secretary, said it was “no longer possible” to put the treaty to a popular vote. “Now that the treaty is going to become European law and is going to enter into force, that means a referendum can no longer prevent the creation of the president of the European Council, the loss of British national vetoes,” he said.

“These things will already have happened and a referendum cannot unwind them or prevent them.”

President Klaus confirmed that he had signed the pact only hours after the text was given the green light by a Czech court which had been asked to rule on its constitutionality.

"I signed the Lisbon Treaty today at 1500," he told reporters in Prague as an aircraft prepared to take the Czech articles of ratification to Rome, where the original treaty setting up the EU was signed.

Mr Klaus was the last EU leader to ratify the treaty, which began life as the EU Constitution, and his signature means the 27 EU member states can pick their first-ever full-time president as well as a new foreign affairs representative.

Across the EU, leaders breathed a collective sigh of relief, from the European Commision president, Jose Manuel Barroso, who said he was "exceptionally satisfied", to the German foreign minister, Guido Westerwelle, who described it as a "good day for Europe."

The flick of the Czech president's fountain pen brings to an end an extraordinary marathon; not since the fierce battles over the Maastricht treaty has a piece of European statecraft stoked up such strong and hostile emotions.

At its heart was public uncertainty about how deeply integrated the European Union should become and public dismay that these decisions were being made overwhelmingly by the political class rather than as the result of open debate.

For the past month – since the Irish approved the treaty in a referendum on October 2 – EU leaders have been behaving as if the Lisbon changes were in place: waging a debate for example on who should become the future European President and the future High Representative on foreign affairs.

Now these virtual discussions are about to become real. The next stage will be a special EU summit later this month; the top jobs including a new Commission line-up, will be agreed.

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