This winter's biggest political story may turn out not to be focused on the Conservatives, Labour or the Lib Dems, but an organisation that until recently was routinely condemned to the fringes, and mocked as a collection of eccentrics and oddballs.

The UK Independence Party has regularly drawn 6 per cent or 7 per cent in the polls, sometimes climbing as high as 11 per cent, but truly entered the mainstream in the run up to the Rotherham byelection in mid-November. The party's prospects were been boosted by a remarkable story in which the local council decided to remove three children from their foster parents when the couple were discovered to be Ukip members. The children are migrants from mainland Europe; Rotherham's director of child services said she had to be mindful of their "cultural and ethnic needs", in the context of Ukip's policies on multiculturalism.

Recently, the Tory MP and party vice-chairman Michael Fabricant published a report titled “The Pact”, in which he suggests an electoral deal between the Conservatives and Ukip, on the basis of a referendum on Britain's EU membership, and offering a place in a future Tory cabinet for Ukip leader Nigel Farage.

The Tory leadership duly poured cold water on his suggestion, but the underlying thinking was hardly revelatory: Ukip's rise is jangling Tory nerves, and with good reason.

Growing support

Ukip already has 12 members of the European Parliament and there are three other ex-Tory Ukip-ers in the House of Lords. The party now has 158 people serving on local councils – though the vast majority are concentrated at town and parish levels – a number regularly swelled by more revolting Tories.

They are all committed to a self-styled "libertarian, non-racist party seeking Britain's withdrawal from the EU," whose ideas are built on the claim that even the Conservatives – and read this bit slowly – "are now Social Democrats", and that the main parties "offer voters no real choice".

Aside from pulling out of Europe, Ukip's other notable positions and policies seem purposely designed to cut across what remains of the metropolitan "modernisation" agenda that Cameron and his supporters brought to modern Tory politics. Chief among them is the belief that climate change is a matter of debate and "wind power is futile", the contention that there should be "real and rigorous cuts in foreign aid" (to be "replaced with free trade", apparently). Given half a chance, Ukip would also freeze "permanent immigration" for five years.

The party's prevailing tilt is in the small-state, cut-spending direction, though it would hold on to Britain's nuclear weapons, and "make increased defence spending a clear priority". It is opposed to gay marriage (though it's OK with civil partnerships), and advocates an end to the ban on smoking in "allocated rooms in public houses, clubs and hotels." The party's radicals also believe in a flat rate of income tax, an idea that has found favour in Serbia, Ukraine, Slovakia, Georgia, and Romania.

In 2006, much to Ukip's fury, Cameron famously called them a party of "fruitcakes, loonies and closet racists", and there have been occasional reports about Ukip members with links to the far right. In the European parliament, their MEPs are part of a grouping called Europe of Freedom and Democracy, which also includes the Italian Northern League, the Lithuanian Order and Justice party, and an outfit from Greece called the Popular Orthodox Rally.

EU and Tory woes

Why has the party's support suddenly ballooned? According to John Curtice, the renowned psephologist and professor of politics at Strathclyde University, the answer is inevitably bound up with two institutions that have each had a grim 2012: the European Union, and the British Conservative party.

"The simple answer is that the public are getting much more eurosceptic," he says. "But it's not clear that it's any more eurosceptic than it was in the late 70s and early 80s. The other argument is, you've got a bunch of people out there who are normally Tory supporters, and they're not entirely sure that Cameron's got it. They've lost confidence in the competence of the Tories. Now, if you're in that situation and you're a voter on the centre-right, where are you going to go?"

In 1991, a London School of Economic historian and academic called Alan Sked formed the Anti-Federalist League, a group-cum-party opposed to the Treaty of Maastricht, the agreement that formally established what we now know as the European Union. Two years later, it became the UK Independence Party.

In 1999, Ukip got its first three MEPs. Five years later, it reached its first watershed moment, when 12 were elected. Nigel Farage, a commodity broker and former Tory, became Ukip leader in September 2006, although he resigned three years later. In November 2010, he once again became Ukip's leader, and is now a firmly embedded part of the culture.

‘Political earthquake’

Paul Nuttall, 35, is a Liverpudlian former academic, an MEP for the north-west region, and is now the Party's deputy leader. He puts their apparent surge down to "being proved right on everything to do with the European Union," and the endless warnings the party has dispensed about "mass, uncontrolled immigration".

In the European elections of 2014, he reminds me, the party's aim is to finish first. At next year's general election, they want nothing less than a "political earthquake", though what that might mean remains unclear.

But why not, I wonder, swallow hard and get with the Fabricant programme? A deal with the Tories, after all, would guarantee them at least one seat in cabinet – and, one assumes, a handful of MPs. "The biggest stumbling block at the moment is the prime minister himself," says Nuttall. "He can't be trusted on the European Union."