David Cameron has reiterated his promise to put the Lisbon Treaty to a referendum in the UK if his party gains power before it is implemented.
The Conservative leader said: ‘There will be no change in our policy on Europe. There will be no change in Conservative policy as long as the Lisbon Treaty is still not in force.
‘I have said repeatedly that I want us to have a referendum. If the treaty is not ratified in all member states and not in force when the election is held, and if we are elected, then we will hold a referendum on it,’ he added.
Ireland passed the Treaty by a margin of 67.1% to 32.9%.
The Czech Republic and Poland are the only two countries who have yet to sign the document.
The British parliament ratified the Lisbon treaty after the Labour government rejected Conservative calls for a referendum, but the Tories say they will reverse Britain's ratification if voters reject it in their planned vote.
Conservative foreign affairs policy chief William Hague said he respected Ireland's decision to accept Lisbon, but said the treaty had ‘no democratic legitimacy’ in Britain.
‘The government now needs to explain why the Irish people have had to vote twice when the British people have not been allowed to vote once,’ he said.
Mr Cameron has said he will set a date for the referendum during campaigning for the British general election next year.
Meanwhile, Czech President Vaclav Klaus has said his country's ratification of the Lisbon Treaty is ‘not on the cards’.
Mr Klaus and Polish President Lech Kaczynski still have to sign the Treaty, which must be approved by all 27 EU countries to take effect.
Mr Kaczynski has said he would sign if the Irish vote yes, but Mr Klaus said the Czech constitutional court had asked him to hold off ratification until it passes a verdict on a complaint against the text made by Czech senators.
‘As you have noticed, I am banned from signing (the Treaty) until the constitutional court comes up with something,’ Mr Klaus said.
The court has said it expects to announce a date for the final ruling within three weeks.
In the meantime, it has ordered Mr Klaus ‘to abstain from any steps that could lead to the ratification...until (it) passes its verdict.’
The complaint by Czech senators has upset the Treaty’s supporters who are afraid about Mr Cameron's referendum plans.
But Mr Klaus said today that ‘the people of Britain should have been doing something much earlier, not just now. It's too late to say something and wait for my decision’.
Commenting on the Irish vote, Mr Klaus said it was ‘tarnished since this is a repeated referendum’.