UKIP have national support of around 16 per cent, say pollsters, a massive increase from the 3 per cent they received at the 2010 general election. Many UKIP supporters are tired of the "old politics" and want their own voices to be heard on the issues that concern them: leaving the EU, immigration control and patriotic self-government.
But are they likely to achieve this? Predicting the results for UKIP is not easy because of their rapid growth. Simple prediction models, based on uniform national swing, assume that UKIP support is spread evenly across the country. This assumption is wrong, and gives no seats at all to UKIP. A much better prediction can be made by using the results of the European Parliament elections in May 2014.
These elections have results broken down by local districts, which are nearly as small as the Westminster constituencies themselves. This gives a good guide to UKIP strength at a local level. Using these data Electoral Calculus has predicted the results of every seat, with a focus on the margin between UKIP and the winning party in each seat.
The map shows every GB seat schematically, each given the same area, and large urban areas have been separated out to prevent distortion. Seats where UKIP are within 25% of the winning party are coloured purple, with stronger colours denoting closer margins. UKIP support is particularly strong in Essex, northern Kent, Lincolnshire and the south west. UKIP is weak in London, Scotland, south Wales and northern metropolitan areas.
Even with this advanced modelling, the outlook for UKIP is bleak. There are only have 5 seats where they are within 10 per cent of winning, and only 27 seats where they are within 15 per cent. By contrast, both Labour and Conservatives have about 100 seats where they are within 15 per cent of winning. In terms of actual seats won, UKIP is currently predicted to win just one seat (Clacton), and to come close in two others (Thanet South and Rochester & Strood).
And this conclusion is not unique to Electoral Calculus. Other electoral forecasters (UK Elect, Elections Etc, Election Forecast, and May2015) all have UKIP winning between one and four seats. Constituency-level polling, conducted by Lord Ashcroft and others, has only ever shown six seats which UKIP might win. And, putting their money where their mouths are, the bookmakers (Ladbrokes, betfair and Paddy Power) have UKIP likely to win at most five seats.
The real challenge to the two-party system comes not from UKIP but from the SNP, which is on track to hold the balance of power. However, if either ex-Tory or ex-Labour UKIP supporters returned to their previous party, then it would have a Commons majority without the SNP. UKIP supporters need to think about which option they prefer.