“All bets are off, the whole thing’s up in the air.” So said Ukip leader Nigel Farage last November after his party won its second by-election in successive months.

In the warm glow of the two triumphs, which elected Ukip’s first two MPs to the Westminster parliament, party officials talked about claiming 20 seats, potentially leaving them as king-makers in the expected coalition negotiations.

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With David Cameron having promised an ‘in/out’ referendum if he remained as prime minister, Ukip votes could guarantee a referendum.

Moreover, a string of by-elections in which Ukip finished a close second in seats once so safe that the Labour vote was weighed rather than counted, suggested that Ukip was tapping into discontented Labour, as well as Conservative voters.

Six months on and the optimism has faded.

Britons go to the polls on Thursday (7 May) and Nigel Farage’s party has quietly conceded that it only has a chance of success in about half a dozen seats.

If Cameron is able to make good on his referendum pledge it will be because he persuaded the usually pro-European Liberal Democrats, and probably others, to trade it for ministerial jobs.

The three seats it is likely to win include Clacton and Rochester, the two constituencies it claimed by-election victories last autumn, while Farage’s target seat of South Thanet has become a 50-50 battle with the Conservatives. All three constituencies are coastal towns in the South-East - Ukip’s traditional heartlands.

So why the failure to launch?

Even in an election campaign where the prime minister is promising to hold an ‘in/out’ referendum if his party is elected, EU membership has not been one of the major issues in the campaign. Despite the average Briton’s reputation for casual euroscepticsm, it never is.

What threatened to make this election different - and which Ukip was banking on - was that immigration, from eastern Europe in particular, would convince voters of the iniquity of EU membership.

While immigration has been among the most frequently raised subject on the doorstep, both Labour and the Conservatives unveiled plans to restrict EU migration and migrants' access to welfare benefits in a bid to head off Ukip.

The 2015 campaign has been strange on many fronts. Not least in the sense that, with the exception of Scotland, the opinion poll numbers have barely moved.

Neither has Farage been on good campaigning form. His main contribution to the set-piece televised debates was to suggest that most patients diagnosed with HIV in Britain each year were foreigners taking advantage of the UK’s free health service, hardly a way to appeal to undecided voters.

Meanwhile, the emergence of the Scottish National party, and its leader Nicola Sturgeon as the new media darling in UK politics, has sidelined Farage, on whose success Ukip is heavily reliant. The SNP is almost certain to provide the big story of Thursday night, sweeping 50, or possibly more, of the Scottish constituencies.

Ukip was always going to find it hard to get a foothold in Westminster. The party’s membership has increased from 30,000 to over 41,000 in eighteen months but its presence in local government remains limited.

When it comes to national elections, with 650 local races, the ‘ground war’ of local campaigning is at least as important as the battle for the airwaves, and Ukip’s is simply not at the same level of effectiveness as its rivals.

In comparison, although the Liberal Democrats may be floundering in national opinion polls - most surveys put them on less than 10 percent - excellent local organisation, despite being depleted by four years of dismal results in municipal elections, will probably enable them to hold onto 30 of the seats they claimed in 2010.

Ukip also look set to be unlucky with parliamentary arithmetic. Their leverage is dependent on a Conservative showing strong enough to be within striking distance of a majority, not the 270-285 seats most polls forecast.

Farage has promised to resign the Ukip leadership “within ten minutes” if he fails to be elected on Thursday night. This threat not come as a huge surprise. Farage has periodically bemoaned the strains on his health and personal finances of being Ukip leader.

Amid their success in by-elections and last year’s European elections, it is easy to forget that Ukip has never come close to winning a seat in a general election. By the standard of previous elections, three seats and 13 percent of the vote would still be a breakthrough, albeit one that falls short of expectations.

In an election where the result is so uncertain, it is also still possible that a handful of Ukip MPs could end up wielding decisive power in the next, fragmented, Parliament.

But on a night where all party leaders bar the SNP’s Nicola Sturgeon have reasons to fear for their job security, it would still be a turnaround, not to mention a demonstration of the fickleness nature of politics, if Farage was to be the first significant casualty.