This week’s allegation in the Daily Mail that Ukip might have covered up an unwelcome poll in South Thanet was the latest development in a seat that is fast turning into the most high profile in the country. A three-way marginal involving a party leader like this is, to my mind, without historical precedent.

Speaking as the Labour candidate for the constituency, I can say that the news that Ukip tried to downplay the outcome of ComRes’s survey is not as surprising as it should be. What we are consistently seeing on the ground in South Thanet is Nigel Farage’s “rotten borough” approach to constituency politics, with repeated absenteeism from local hustings and debates. The revelation that he was trying to hype his way into parliament does not come as a shock.

Thanet is a fundamentally decent place, and outbursts like Farage’s on HIV make many voters deeply suspicious

The really interesting thing about the poll is quite how wide open it confirms South Thanet to be. Just two points separate Labour, Ukip and the Tories. This will go right to the wire. Given how tight the race here was always looking, I have never been able to understand the Conservatives’ choice of candidate. Craig Mackinlay is a former leader of Ukip, and has come under pressure to assure voters he will not switch back once elected. Some have identified his selection as a smart move by the Conservatives, triangulating the Farage threat – but to me it is their biggest error. Who on the political hard right is going to vote for Robin when they have Batman on the ballot paper?

Indeed, my impression from speaking to people on the doorsteps is that opting for a Ukip-lite candidate has been counterproductive for the Tories. Thanet is a fundamentally decent place, and outbursts like Farage’s on HIV make those voters who are not already card-carrying Kippers deeply suspicious of anything tainted by Ukip association.

This is why we have recently been seeing significant numbers of Conservative voters shift to Labour in South Thanet. And it is why we will this week be sending out a letter to voters in Tory areas, who may traditionally have been “one nation” Conservatives, but who are switched off by the chauvinism and aggression of the Ukip-Tory race to the bottom.

In a certain respect the decision to choose a former Ukip candidate replicates in miniature the steady drift to the right that we have seen from the Conservatives nationally. David Cameron, who once played the moderniser, has allowed his party to be dragged back to the days of hard line nasty party policies over the past five years. Indeed, the contrast between the Conservatives’ 2015 candidate in South Thanet and their 2010 one – the clubbable one nation Cameroon, Laura Sandys – could not be more stark.

Nigel Farage calls on Ukip members to bolster South Thanet campaign Read more

South Thanet has been described by some as a maverick seat in this election – a constituency that defies categorisation and gives little sense of which way the wider political winds are blowing. But for me it is more of a bellwether than ever – and not just for the next five years, but for the next 15 or 20.

Farage’s announcement that he will stand down if he loses, means this is the election where Ukip will either become a permanent fixture or make a quiet exit. It is a chance to stop Farage, and establish a positive, progressive consensus, for Thanet and for the country – rather than succumbing to the inexorable drift right-wards. What we could see is the “Portillo moment” to end all Portillo moments.

The Conservatives forfeited the chance to lead the charge on this, by opting for just a paler shade of purple. But Labour is countering Farage every step of the way. And, as yesterday’s poll showed, there is still everything to play for.