Douglas Carswell, former Conservative MP for Clacton-on-Sea, defected to UKIP on the 28th of August and resigned as an MP on the 29th – an expected surprise. Carswell has claimed that Cameron is “not serious about change” and that only UKIP can force real change as grinning UKIP leader Nigel Farage joined his prize capture for a constituency walkabout. My question is: how will this change Westminster politics in the months before the General Election, especially for the Tories?

Carswell said “”I stab people in the front, not the back” as he defended his decision to quit the Conservative party. He insists that the Prime Minister’s secret plan is to renegotiate with the EU “just enough” to be able to claim that Britain’s relationship with it has changed sufficiently to justify campaigning to remain a member in the 2017 referendum. He has reasoned that UKIP will bring an end to this variety of insincere Euroscepticism.

However many critics have brought forth cases which display a hint of hypocrisy, including his praise for Cameron’s promise of an EU referendum and this quote from the Daily Telegraph (15 April 2014) in which he said “In order to exit the EU, we need David Cameron to be Prime Minister in 2017 – the year when we will get the in/out referendum, our chance to vote to leave the EU.”

The prime minister has said that it was “odd” and “self-defeating” for a committed Eurosceptic to stand down and reject the only party that had a realistic chance of staging the in/out vote on the EU membership he craved.

Carswell will almost certainly win the by-election in Clacton-on-Sea, where he has not only got an estimated personal vote of 9,000 but is also where almost twice as many people voted UKIP (48 percent) as opposed to Conservative (25 percent) with the seaside seat’s greyer voters likely to win UKIP its first MP.

If Carswell is successful then this can be considered a serious blow to the Prime Minister. Polling by Lord Ashcroft, a Tory peer, suggests that 52 percent of people who backed UKIP in this year’s European elections were former Conservatives, meaning that the Tory campaign is in danger of being derailed by right-wing rebellion. In private, Cameron admits that “bringing home” a significant number of UKIP supporters is a necessary condition for victory in the General Election.

There are rumours of more Eurosceptic Conservatives considering defecting to UKIP, and if Carswell wins other MPs who fear defeat at the election may be tempted, rebranding UKIP into “the conservative party in exile”, in Peter Oborne’s resonant phrase. Though I expect that some Tory Eurosceptics will use Carswell’s defection to tighten the noose on Cameron, rather than defecting themselves. At the time of Carswell’s announcements even those MPs who were saying Carswell had made a mistake were pressuring Cameron to explain further details of his reform.

In one swoop UKIP have recaptured the political narrative; “those who predicted we would lose momentum heading into the 2015 election are going to have to think again” boasted Nigel Farage in his article for the Independent. Although senior Eurosceptic Tories denied he was the first of many, with John Redwood saying the “so-called eight” were “a figment of Ukip’s imagination”, UKIP’s  Treasurer Stuart Wheeler, who wines and dines Tory Eurosceptics often, says he has had discussions with eight Tory backbenchers. He has declined to name names – but possible defectors may include Philip Hollobone, Nadine Dorres and Philip Davies (although Davies has recently said that “I’ve always told Douglas (Carswell) that he is not a true Conservative, he is an anarchist or communist.”

Another change this decision may inspire is the split in the sceptic vote – between Conservative and UKIP. For example, ‘blood brothers’ Dan Hannan, Tory MEP, and Carswell now sit on either side of the sceptic fence. Hannan now claims that “the split in British Euroscepticism is ruinous, and may get worse before it gets better. As things stand, Ed Miliband will become prime minister on a pitifully low share of the vote, we’ll be back to tax-spend-and-borrow, our referendum will be cancelled and European integration will accelerate.” Hannan is frequently asked why he has not defected to UKIP, and he has stated that changes within UKIP has meant that the the party has adopted a spread of domestic policies aimed at picking up disillusioned voters, so according to Hannan “it is no longer focused on getting out of the EU and, in consequence, is prepared to subordinate that goal to its wider electoral interests”.

Crucially, a strong UKIP result in 2015 could deny Cameron a majority and put Ed Miliband in No 10. Firstly, Carswell is offering Labour the opportunity to highlight every Tory split as evidence of their unfitness to govern and portray every utterance from Number 10 as a lurch to the right or of policy-making dictated by Nigel Farage. Secondly, in a close election the combination of UKIP’s East coast gains, UKIP gains in Tory marginal constituencies, and extra Tory losses to Labour, could decide whether Labour or the Conservatives end up as the largest party. In other words, Carswell’s almost certain by-election triumph could lead to Ed Miliband becoming Prime Minister—and destroying any prospect of a referendum on Britain’s membership of the European Union.

Asked whether he was worried that Tory defections to Ukip would help the Labour leader, Ed Miliband, win the keys to Downing Street in next year’s general election, Carswell said: “I don’t really see the difference between either front bench. That’s why I am doing this. What would be the difference between his gang being on the sofas of No 10 and the current gang?” But perhaps Carswell’s slightly romantic and radical behaviour has, in fact, made his end goal far less probable.

On the other hand, Carswell’s defection has slightly improved the image of British politics. “In an age which habitually puts the worst possible construction on what politicians do, Douglas has reminded us that it’s possible to act purely from conviction” praised Hannan. For other Eurosceptic Conservatives, the threat of UKIP may lead to further reform from Cameron after the Prime Minister’s decision to promise a referendum on EU membership, tighter immigration rules and the prospect of curbs on European migrants. This is, after all, how politics should work in a representative democracy: voters use their choice between parties to signal their desires and preferences; parties respond by trying to satisfy those demands.