On Rochester High Street people are fed up to the back teeth of being confronted by politicians and their hangers-on. For most of them, Thursday’s byelection cannot come soon enough – and they say so in no uncertain terms.

However, John Baldock, owner of Sweet Expectations, claimed as the UK’s only vegetarian confectionery store, has happily turned the frenzy of political and media activity to his commercial advantage. In his shop window are six jars, one for each of the five main parties, and one for the don’t knows. Everyone who comes in is asked who they intend to vote for, if anyone.

Baldock then drops an appropriately coloured bonbon – blue for Tories, red for Labour, and so on – into the appropriate jar. Over the past few weeks, as Ukip’s purple pile has grown the fastest, Baldock says he has become something of a political expert. He has a hunch that the byelection could be tighter than his rivals, the professional pollsters, claim. “Labour would have done a lot better if they had been more active, but we have hardly had any Labour people in,” he says. “A lot of customers are saying they will vote Conservative to keep Ukip out. I think it could still be quite close.”

In sixth place on Thursday morning, with a sad tally of just nine yellow bonbons, were the Lib Dems. “The Liberal Democrats? Well, they are doing dreadfully,” says Baldock. “And two of the nine were from people who said they felt sorry for them!” His customer poll is not exactly scientific, but it roughly mirrors the results to date in official surveys by the likes of YouGov. It is the talk of the High Street – a local man’s record of the way voters are turning away from the established parties in droves.

Facebook Twitter Pinterest John Baldock’s unscientific but surprisingly accurate sweet poll. Photograph: Antonio Olmos for the Observer

With just days to go until the Rochester and Strood vote, the real pollsters agree that Ukip is on course for another sensational result. The Conservatives took this north Kent seat from Labour at the 2010 general election with a hefty majority of 9,953. But Nigel Farage’s party, which did not even stand here at the last election, looks likely to oust the Tories from what they thought had become a safe southern stronghold.

Farage says he is “confident but not complacent” about the result. He told the Observer that this byelection was the most important since Roy Jenkins won Glasgow Hillhead for the SDP in 1982. If his anti-EU party wins in this corner of Kent and installs Tory defector Mark Reckless as its second MP in Westminster, the Ukip leader believes it will “completely change the arithmetic of British politics”.

He predicts that more defections will follow – most from the Tories, but perhaps one or two from Labour. That is because Ukip will have proved that it can destroy the established parties in their previously solid heartlands.

When Reckless defected in September, the Tories were confident of holding Rochester, saying it was more predictably and solidly Conservative than Clacton, where the defector Douglas Carswell won the first seat for Ukip last month. “Personally I think that if we win well on Thursday, it will be different. This is not an ‘end of the line’ place like Clacton,” said Farage. “There will be MPs sitting in constituencies with a particular socioeconomic makeup, on a blue badge, who will say to themselves on Friday that we are pretty doomed on this approach and we are better off on a Ukip ticket.”

Up and down the country his party is taking support not just from the Tories but also from Labour, the Lib Dems, and even people who used to be non-voters. He now believes Ukip could win as many as 20 seats at the next election, double what he thought a few weeks ago. It could then hold the balance of power in a hung parliament. Psychologically, Thursday would be crucial. “It is very, very important for us and for the Conservatives. If Cameron, who has thrown the kitchen sink at this election, can’t hold the seat, he will begin to look like a loser.”

The prime minister has tried his best to hold back the Ukip tide. He has visited Rochester and Strood four times already. Until recently there was a convention that prime ministers stayed away from byelections. But with Clacton having already fallen, this one was simply too important. He had to stop the rot. However, such is the strength of the anti-politics mood that the tactic of “love-bombing” seems, if anything, to have backfired. Rochester and Strood is full of people who not only distrust mainstream politicians but seem to have become hostile to their advances.

“Excuse my English, but I am pissed off with the Tories. They are everywhere here, and what have they done for me?” asks John Anderson, a middle-aged man on sickness benefits. A local businessman queueing at a cash machine says the whole town is heartily sick of their visitors from Westminster and their sidekicks. “Every 10 yards there is someone with a rosette on. We just want it to return to normal,” he says. Labour’s candidate, Naushabah Khan, 28, a PR consultant, finds the occasional supporter as she knocks on doors in a Labour ward in Strood and makes much of her backing for the local hospital, but just as many really don’t want to know. “None of your business,” says an elderly man who shuts the door firmly on a canvasser when asked how he intends to vote.

Facebook Twitter Pinterest Mark Reckless, the UKIP candidate for the Rochester and Strood byelection, in front of his party’s offices on the High Street in Rochester. Photograph: Antonio Olmos for the Observer

Everywhere the old order is being challenged, as the parties with recent experience of government are losing ground to the newcomers. A local poll last week by Lord Ashcroft put the surging Greens on 5%, well ahead of the Liberal Democrats on 2%. The Greens’ candidate, Clive Gregory, says he believes his party could even come close to Labour, which was on 17% in Ashcroft’s survey. “If we can get people to hold to what they say, then we could get to 6% or 8% and higher, and that would mean a lot of votes were coming from Labour,” says Gregory. Natalie Bennett, the Green party leader, says: “Politics is changing so fast it is difficult to know what is going to happen.”

If the Greens were to pip Labour into fourth place, it would be nothing less than cataclysmic for Labour and Ed Miliband’s leadership.

The loneliest souls in Rochester and Strood are the virtually invisible Liberal Democrats, past masters of blitzing target seats during byelections. Their candidate, Geoff Juby, a local councillor, admitted that many Labour-leaning Lib Dems thought the party had “lost its soul” on issues such as tuition fees. It had, he added, also run too short of money to support a byelection in a seat like Rochester and Strood with a general election just around the corner.

On Thursday, a small group of supporters came from London to lend Juby a hand, but they were busy lowering, not raising, expectations for any media representative who bothered to come to see them. Among the team down for the day was Baron Newby of Rothwell, the deputy Lib Dem chief whip in the House of Lords, who when asked how his party would fare, freely admitted that they would struggle to hold on to their deposit.

Back at Sweet Expectations, Baldock offered a glimmer of new hope for the poor Liberal Democrats. He had put in two more yellow bonbons in the past three hours. “It’s going wild,” he said, laughing in the street.