Nigel Farage, leader of the UK Independence Party, or UKIP, has rarely been photographed without a pint of beer in his hand over the last few years as he’s caroused his way around Britain, taunting its political establishment. And he had good reason to raise a glass over the weekend as UKIP won elections to the European Parliament, becoming the first party other than Labour or the Conservatives to win a UK national election for more than 100 years.

Long dismissed by mainstream politicians and commentators as oddballs and extremists – Conservative Prime Minister David Cameron famously dismissed them as “fruitcakes, loonies and closet racists” – Farage’s insurgents have become increasingly hard to ignore. UKIP wants an end to mass immigration to the UK, and Britain’s withdrawal from the European Union – the two issues are inextricably linked, as EU rules mean Britain is unable to control immigration from other member countries.

The result didn’t come as a big surprise – several polls had put UKIP narrowly ahead of Labour in recent weeks, and in the event UKIP took 27.5 percent of the vote, with Labour second at 25.4 percent and the Tories third at 24 percent. But it’s the most significant development in British politics in decades; Farage hailed the result as “an earthquake,” and predicted that his party would win seats in next year’s general election.

The Conservatives did better than expected, suggesting that some Tory defectors to UKIP are being lured back by the steadily recovering UK economy. But another strong showing by UKIP in 2015 would likely condemn  Cameron and his party to defeat at the hands of Labour, and some Tory MPs have renewed calls for an electoral pact with UKIP to avert disaster. Farage, meanwhile, insists the Tories can’t win the election if Cameron remains in charge.

Cameron has been eager to persuade disaffected Tories that he feels their pain. Last week he said he shared the frustration of voters over his party’s inability to control immigration, and arriving in Brussels this week for a meeting with other European leaders to discuss the election results, which saw gains for populist parties from both the left and right across the continent, he said the EU had become “too big, too bossy, too interfering”.

The results across Europe will strengthen Cameron’s hand as he seeks to make the case for EU reform, and for the return of key powers to national governments, ahead of the in/out referendum on EU membership that he’s pledged to hold if the Conservatives secure an overall majority in 2015. Labour, and the Liberal Democrats – who are the Tories’ partners in Britain’s coalition government – have refused to hold a referendum on Europe.

While trying not to appear dismissive of voters’ concerns, the established parties are clinging to the hope that UKIP remains a protest party, and that many of those who voted for Farage will desert him when the “real” election comes along. While UKIP dismisses those claims, there’s undeniably a protest element to UKIP’s support – when general election voting intentions are polled, UKIP’s support falls to around half the level it achieved in the Euro elections. However, even that would be enough for UKIP to have a major influence on who forms the next government.