If the normally reliable Tim Montgomerie is right then several Tory MPs are on the verge of defecting to Nigel Farage's UKIP. Although UKIP has never come close to winning a Westminster seat, and boasts just one MP defector - Bob Spink - since its formation in the late 1990s, it's not a surprise that a handful of euro-obsessed Tory MPs are thinking about defection. More serious for the Tories is UKIP's emergence as a viable challenger to the Lib Dems in national elections. The party has been consistently polling between 7-10 per cent in the last few months which, while almost certainly not enough to win a seat in the Commons, is more than enough to deny the Tories a handful of marginal constituencies and, potentially, a Commons majority.

Just as George Galloway’s upset victory in Bradford should shake any complacency in Labour that they will be the automatic beneficiaries of rising public anger against government and the political class, the Tories cannot afford to dismiss of UKIP out of hand. It’s actually not hard to see why UKIP carries appeal. Nigel Farage is a witty and fluent speaker and he speaks to an old-fashioned breed of reactionary nationalism combined with social and fiscal conservatism which can still be found in conservative clubs and associations up and down the country.

Meanwhile, with the EU facing an almost existential crisis over the future of the single currency and most countries either in recession or on the brink, it is a great time to be a Eurosceptic. Indeed, the performances of Marine Le Pen and Jean-Luc Melanchon in France have shown that anti-establishment parties of the extreme-right and hard-left carry plenty of appeal to voters fed up with a political establishment that has landed them with debts, deficits and austerity-driven recession. With the Lib Dems having given up their status as a protest vote party by nailing their colours to the Tory, UKIP has plenty of fertile ground at its disposal.

Outside European elections, where UKIP can campaign on its raison d’etre and pick up eurosceptic votes from all of the three main parties, its vote share poses a lot more threat to the Tories than Labour or the Lib Dems. Indeed, around 60 per cent of UKIP voters are disaffected Tories. In 1997 a number of Tory MPs fell to small majorities where the Referendum Party candidate got more votes than the majority and in 2005, as well, UKIP votes cost the Tories a handful of seats.

Although they are now well-placed to pick up protest votes, the truth is that UKIP is the product of the Conservative party's unhealthy obsession with the EU which, nearly twenty years after Maastricht, is still no closer to being resolved. There is very little difference between Farage and the Tory Maastricht rebels of the early 1990s, or even Jimmy Goldsmith's Referendum Party which took 3 oer cent of the vote at the 1997 election.

David Cameron is also the perfect Tory leader for UKIP. Having won the party leadership in 2005 with the support of many Eurosceptics after having promised to take the Tories out of the European People's Party - the party group for centre-right parties across Europe - he has attempted the impossible task of placating both ardent Eurosceptics and moderates. Hence, Cameron opposed the Lisbon Treaty but ruled out tearing it up and re-negotiating and has made no serious attempt to win any opt-outs or derogations. In coalition with the pro-European Lib Dems his balancing act is even tougher and the bizarre ‘non-veto' at the December EU summit achieved the double whammy of upsetting the Lib Dems and, when they realised that Cameron hadn't actually blocked or won anything, the Tory back-benches.

Cameron’s insoluble problem is that his Eurosceptics will be disappointed by anything less than British withdrawal from the EU or, at the very least, radical re-negotiation of Britain's membership. The chances of EU withdrawal are zero and, having burnt most of his remaining political bridges at the December summit, there is no virtually no chance of other European leaders agreeing to re-negotiation. All of which is manna from heaven to UKIP.

The main problem that UKIP face – and which is the reason why, outside of the European elections, the party has little prospect of a breakthrough - is a lack of money and activists. With around 15,000 members across the UK and no big donors they simply don't have the cash or shoe-leather to contest more than a handful of seats. Moreover, like most fringe parties they are a one-man band, which is just as well because aside from Farage there is very little talent in their ranks.

The other benefit of being small is a lack of scrutiny. With no chance of ever winning seats outside the European Parliament, its party policy and politicians are little known and little discussed. Since two of the 12 UKIP MEPs elected in 2004 have since been jailed for fraud and the party continues to be dogged by allegations of racism, sexism and homophobia, this is no bad thing for UKIP.

But while they may be small, UKIP deserve to be taken seriously. They outpolled Labour and the Lib Dems in the last European elections and, while the euro crisis continues, they have every chance of beating the Tories in 2014. Domestically, they pose a small but deceptively serious problem for the Tories – not big enough to win seats for themselves, but certainly big enough to sink the prospects of a Tory majority. Frustratingly for the Tories, the rise of UKIP is almost entirely self-inflicted.

Benjamin Fox is political adviser to the Socialist and Democrat group in the European Parliament