Vanessa Mock: Now the fate of the treaty lies in Czech hands

Ireland may be in the bag but now Brussels is fretting about the Czech threat to the Lisbon Treaty.

The Czech Republic's famously eurosceptic president, Vaclav Klaus, has vowed to delay ratification of the treaty, leaving his country as the last remaining hurdle in the way of the document coming into force by the start of next year.

The worst-case scenario, diplomats say, is for Mr Klaus to hold out long enough for the Conservatives to come into power next spring and then strike a deal with David Cameron to sink the project for good. The Tory leader wrote to Mr Klaus last week, reassuring him that, if he delayed proceedings, he would stage a referendum in Britain if he came to power.

"It is hard to say just how far Mr Klaus is prepared to go. He's an unpredictable character with a huge sense of national pride," said one diplomat in Brussels. "But he is looking isolated," the diplomat added, echoing the widespread belief in Brussels that "Cameron's appetite for a referendum is fading."

Irish voters returned to polling stations on Friday for a re-run of a referendum on the treaty which was torpedoed last year by fears over abortion, conscription into an EU army and loss of sovereignty. EU officials wore broad smiles and green ties in Brussels on Saturday when results showed a 20 per cent swing to the Yes side, with 67.1 per cent voting in favour.

The Polish President, Lech Kaczynski, the only other EU leader who still needs to sign the document, has indicated his intention to do so soon and diplomatic machinery is being cranked up in order to raise the pressure on Mr Klaus. The pro-European Czech Prime Minister, Jan Fischer, is flying to Brussels on Wednesday, the same day that Sweden, which currently heads up the rotating EU Presidency, will dispatch its Europe minister, Cecilia Malmstrom, to Prague to "assess the situation".

"It's a race against the clock," said another EU source. "We have to get the Czechs out of the way so we can speed ahead with the really big changes in Europe," he said, referring to a string of innovations enshrined in the Lisbon Treaty including the creation of an EU presidency and a powerful new foreign policy chief. Former British prime minister Tony Blair is one of the names in the frame for the top job and the Swedish presidency is desperate to announce the candidates during a summit of EU leaders at the end of October so that the treaty can come into force by 1 January 2010, as originally planned.

But all this now rests with Mr Klaus, whose hand has been strengthened by 17 conservative senators who filed a fresh legal complaint against the treaty to the country's Constitutional Court last week. "I will wait for the Constitutional Court's verdict," Mr Klaus said on Saturday. However, diplomats believe that the court is unlikely to uphold the complaint and, with both houses of the Czech parliament already having approved the treaty, Mr Klaus will struggle to continue bullishly to stand his ground.

The President of the European Commission, Jose Manuel Barroso, said that "our member states have practically approved the Lisbon Treaty" and said he was confident that Mr Klaus would sign the treaty "in the end".