Europe was plunged into political turmoil last night after Ireland decisively rejected the Lisbon Treaty.

David Cameron, the Conservative leader, insisted the public had clearly said no to further EU integration and called on the "elites in Brussels" to heed its message. However, Jose Manuel Barroso, president of the European Commission, defiantly insisted the treaty was "not dead" and urged member states to continue the ratification process.

Last night, the UK Government made clear it would do just that; next week, the parliamentary process is due to be completed in the House of Lords.

"It is right that we continue with our process and take up the Irish offer of further discussions about the next steps forward," said David Miliband, the Foreign Secretary, adding that Ireland's decision needed to be "respected and digested".

The treaty would bring in reforms to create an elected EU president, an EU foreign minister and would reduce the number of national vetoes. So far 18 out of 27 member states have ratified it through their parliaments but, because of its constitution, Ireland had to go directly to the people for ratification.

Attention will now turn to next Thursday and Friday's EU summit in Brussels when Gordon Brown and his fellow EU leaders will begin the process of trying to work out the way ahead. However, none of the options will look politically palatable to them: scrapping the treaty; changing it or asking the Irish to vote again like they did on the Nice Treaty in 2002.

As the vote was read out in Dublin Castle, campaigners against the treaty cheered and hugged each other. The final referendum result showed 53.4% had voted no while 46.6% had voted yes; turnout was 55%.

The result was a terrible blow to Ireland's political establishment, where all three main political parties, representing 90% of the voters, had urged them to back the treaty.

However, the biggest embarrassment was that of the new Taoiseach, Brian Cowen, facing his first big political test. His government had spent millions of euros trying to beat the "no" campaign, comprised of a small collection of anti-treaty groups, including Sinn Fein.

A downbeat Mr Cowen declared: "We are in uncertain waters. There is no quick fix here." However, he said the EU had been here before and had found a way forward. "I hope we can do so again," he added.

Gerry Adams, Sinn Fein's president, said the battle between the "yes" and "no" camps had been a David and Goliath struggle but "in this case Goliath lost again". Declan Ganley of Libertas, the anti-treaty lobby group, said it was a "great day to be Irish".

In Brussels, Nigel Farage, leader of the anti-EU UKIP, noted how the only people who had had a public voice on the treaty had "kicked it into the long grass".

The "no" camp benefited from depicting the treaty as the thin end of a wedge that could pave the way for reforms on taxation and military neutrality, which Ireland would be unable to block.

Mr Cameron expressed delight at Ireland's rejection and called on the Prime Minister to abandon the ratification process. He said: "By all rights now, it should be declared dead. The French said no to it, the Dutch said no to it, then it was brought back and the only people who have been given a chance to pass judgment on it, the Irish, have now said no to it."

Edward Davey for the pro-treaty Liberal Democrats expressed disappointment at the Irish vote but warned against a political fix in Brussels.

"The Liberal Democrats would certainly not support some sort of back-door, smoke-filled-room deal to try to get this through," he said.