PRAGUE: Czech President Vaclav Klaus said he had finally inked the European Union's reforming Lisbon Treaty on Tuesday, becoming the last EU leader to sign the landmark document into law.

'I announce that I signed the Lisbon Treaty at 1500 (1400 GMT) today,' the ardent eurosceptic said at a briefing, just hours after the top Czech court ruled the accord was in line with the country's constitution.

Czech Prime Minister Jan Fischer then counter-signed the treaty which can now take effect as of next month.

'The Lisbon Treaty ratification process has ended,' Fischer's spokesman Roman Prorok told AFP.

The ratification unties the 27-nation EU's hands to appoint a new European Commission -- its executive arm -- as well as fill the freshly-created posts of president and foreign affairs supremo.

'I hope that now all the obstacles are removed and you'll have this Lisbon treaty coming to force,' European Commission chief Jose Manuel Barroso said in Washington shortly before attending an EU-US summit.

'I think that the transformational potential that is there, the new external profile for the European Union, will be felt immediately,' he added.

The Lisbon Treaty is designed to smooth the workings of the EU, which has almost doubled in size to 27 nations since a swathe of ex-communist nations including the Czech Republic joined in 2004.

The treaty had to be ratified by all members before coming into force.

The delay in implementation has hampered the work of the European Commission, whose mandate expired at the end of October, and put on ice the appointment process for the two top EU jobs created by the treaty.

Belgian Prime Minister Herman van Rompuy has been mentioned as a consensual candidate for president after support for former British Prime Minister Tony Blair proved weak at an EU summit last week.

Britain's current Prime Minister Gordon Brown on Tuesday welcomed Klaus's decision to sign, saying it 'marks an important and historic step for all of Europe.'

'Today is a day when Europe looks forward, when it sets aside years of debate on its institutions, and moves to take strong and collective action on the issues that matter most to European citizens: security, climate change, jobs and growth,' Brown said.

Klaus, who describes the treaty as a threat to Czech sovereignty and refuses to fly the EU flag at his residence, hit out again Tuesday.

'Good cloudy afternoon,' he said in a grim voice before telling reporters he disagreed with the constitutional court ruling that paved the way for him to sign.

'I expected the court ruling and I respect it, although I disagree with its contents and reasoning,' Klaus said, calling the verdict 'a biased political defence of the Lisbon Treaty.'

'I cannot agree with its contents since after the validation of the Lisbon Treaty... the Czech Republic will cease to be a sovereign state,' he added.

Czech lawmakers approved the treaty earlier this year, but Klaus refused to sign pending the top court's verdict on a complaint by pro-Klaus senators. The court had in any case ordered him to wait until it ruled.

After Ireland's two referendums on the treaty and with renewed agonising over Europe in Britain, EU leaders were anxiously waiting for Klaus to end the impasse.

At a summit last week, they agreed to give Prague an opt-out from parts of the treaty, demanded by Klaus in what critics saw as another attempt to delay the ratification.

Klaus had asked for an exemption to ensure the treaty would not allow ethnic Germans forced out of his country after World War II on charges of Nazi collaboration to take legal action to reclaim their property.

Backers of the treaty got more good news on Tuesday as a British newspaper said main opposition leader David Cameron -- widely tipped to be the next prime minister -- will drop plans for a referendum on it.

The Conservative Party leader will shortly announce he will abandon a pledge to hold a vote on the treaty if his party wins the next general election and the document has not been ratified, the Daily Telegraph said.

Cameron had written to the Czech president urging him to delay ratifying the treaty, sparking anger from the leaders of France, Germany and Spain, media reports said last week.