By defecting to the UK Independence Party, Douglas Carswell has almost certainly handed Ukip its first elected member of parliament. Since his announcement, two opinion polls present an incredibly bleak picture for the Conservative party, which could once count on Clacton as one of its safest seats. Survation puts Ukip on a remarkable 64 per cent, an astonishing 44 points ahead of the Tories and prompting some newspapers to talk of an impending "bloodbath". Polling by Lord Ashcroft predicts a similarly depressing result for the Tories, putting Ukip on 56 per cent and 32 points ahead. Ukip was supposed to wither and die over the summer. Instead, and in one stroke, Nigel Farage has pushed his party back into the forefront of British politics.
Ukip was confident about Clacton long before these polls. Carswell's defection had been a long time coming, was known to less than half-a-dozen activists and so Farage had complete control over the story. How the news broke was almost as interesting as the news itself, and will be covered in detail in my next book.
Interestingly, Carswell had also been present at a meeting in parliament where we shared our research with the Conservative party back in April, and when we noted how Clacton had more "Ukip-friendly" voters than any other seat in the country (we will present research to anyone who asks). This helps explain the reaction that Carswell has since received in Clacton. "I'm telling you", said Farage during an interview with the author, "the combination of Ukip and Carswell is like nothing we have ever seen". Similar sentiments were voiced by an organiser on the ground, who reflected after his first day of campaigning: "It was like a religious experience. People running across the street to shake Carswell's hand and praising his decision. I've campaigned for years and never seen anything like it".
But if all of this is true and Carswell does deliver a convincing victory, then what will be the impact of all this on Ukip? As part of a new book on the 2015 general election, I have been following Ukip closely on the campaign trail, spending much of last week with the party as these events unfolded. Based on these observations it strikes me that the impact of Clacton will be three-fold.
A first point centres on credibility. The biggest challenge facing Ukip is no longer organisational. Over the summer, Farage has delegated responsibility, established a "front bench" and covered his flank by improving candidate screening. His primary challenge now is tackling the "wasted vote syndrome"; a belief among voters that smaller parties like Ukip are not credible under first-past-the-post. It is a crushing disease, having ended dozens of political insurgencies before they even got going. A convincing win in Clacton will help Farage to begin to remedy this syndrome. This side of Christmas we may be hearing lots about how Clacton proves that "if you vote for Ukip, you get Ukip".
But this impact might also be more specific. It is a lucky coincidence for Ukip that the one MP who decided to defect is also based in its emerging heartland: the east coast of England. This means that success in Clacton will arrive in the same orbit of seats that offers Ukip its strongest prospects. It will instantly energise campaigns in Essex, Cambridgeshire and Norfolk, where branches are probably already sending activists into Clacton to watch and learn from Carswell's operation. "Ukip winning here", may be planted on leaflets across this region. For the main parties the risk is obvious: a domino effect along the eastern half of England.
A second point concerns the all-important business of targeting. Electorally, Ukip's strength is rooted in its potential to rally a relatively broad church of voters: disillusioned Conservatives in the south, blue-collar voters further north, non-voters who abandoned politics after 1997, and the increasingly important protest wing of the Liberal Democrats. In this respect, some argue that Carswell is a mixed blessing for Ukip. While he might bring elected representation he could also upset a delicate balance in the small party between those disgruntled Tories in the southern shires who look a lot like Carswell, and a "purple collar" faction who are pushing Ukip to target left-behind voters in Labour's northern heartlands. This is a complete misreading of Ukip.
This view not only exaggerates the level of factionalism inside Ukip but misunderstands Carswell. Once upon a time, Ukip may well have balanced precariously on different factions, but since 2010 there has emerged a clear consensus in the party over the need to present a broader line of attack. Carswell himself is emblematic of this "broad church" approach, having had to pitch to different groups in Clacton and recognising the need to make an offer to voters who do not get excited about the EU but do feel intensely angry about an Oxbridge-educated elite that seems not to care about them feeling left behind.
And there is some evidence to suggest that Carswell will help Ukip with this coalition. In the Lord Ashcroft poll from Clacton, Ukip has a healthier gender split, is performing better than average across all age groups and is winning over more 2010 Labour and Liberal Democrat voters. Ukip still faces serious challenges, but Carswell's wider appeal will not have gone unnoticed. Will his arrival encourage a broadening of Ukip's anti-establishment narrative? Will his campaign provide a template for how Ukip attempts to rally this wider coalition in 2015, and will the lessons of the Clacton campaign be transplanted into other key targets?
The final point is leadership. Some journalists portray Carswell as a possible rival to Farage, whose four-year term as Ukip's leader is up for renewal in November. But this is also a misreading. Carswell has little incentive to play intra-party politics. He is not personally ambitious in the same way that other politicians are, and did not need to defect in order to save his seat. From hereon he will be content to concentrate on Clacton, and enjoy an elevated stage on which he can share his ideas about political reform and the state of modern-day conservatism. This is why his real significance as a leadership figure for Ukip lies outside of the party. As a respected voice in centre-right circles Carswell could become a crucial weapon in Ukip's arsenal, touring Conservative seats and urging activist foot soldiers from his old party to follow suit by deserting Cameron. Political pundits obsess about defections at the level of MPs, often ignoring the crucial question of whether Ukip actually wants that particular MP. But arguably it is at the activist level where mass defections would seriously damage the Conservative party while bringing further campaigning experience to Ukip.
Ultimately, only time will tell whether these three consequences come to pass. But make no mistake; Clacton may come to be seen as a crucial watershed in the history of the UK Independence Party.
Matthew Goodwin is Associate Professor in Political Science at the University of Nottingham and Associate Fellow at Chatham House. He is co-author, with Robert Ford, of Revolt on the Right: Explaining Support for the Radical Right in Britain. He tweets @GoodwinMJ