Parties of the populist right may not win any seats in the general election, but the votes they take could be quite crucial in marginal seats where they could exceed the margin of victory for either party. Although I don't have any data to hand on this, my impression has been that UKIP has tended to appeal to broadly middle class voters who might otherwise vote Conservative.
UKIP have also been very much focused on the issue of Britain's relationship with the EU which has worked well for them in European elections, but the narrowness of their focus has been a handicap in general elections (where voters, up to now at any rate, have been inclined to revert to the main parties). They are now seeking to broaden their appeal to working class voters: UKIP
The Conservatives might have grounds for concern about this, although it is noticeable that they are taking a stronger line on immigration and a report in the Sunday Times yesterday suggested that this might be helping them in key seats. The overall 9 per cent lead for them in the YouGov poll is not as large as they need to be really confident of a solid overall majority, even if they are doing better in marginal seats.
Although it is difficult to generalise, the BNP vote has often come from those who would otherwise vote Labour or might not vote at all. A report in The Times in their interesting 'broken Britain' series in which writers re-visit their old home times tried to get beyond the usual clichés about racism as the single explanation to explore what was happening in Burnley, a town where the BNP has done relatively well. You can read the article here: Burnley
For those who do not know Burnley, it is important to emphasise that this former textile town suffers from serious economic and social deprivation. I have seen scenes of urban devastation there that are more characteristic of the United States. One couple referred to in the article had low paid jobs and were struggling to pay a mortgage on a house that was declining in value. These are the very 'working poor' that Labour claimed it would help.
Those interviewed were inclined to blame Mrs Thatcher and Labour deserting the working class for the plight of Burnley. One thing that wasn't mentioned was 'globalisation', but however much people dispute the concept, it is a reality which has hit those with limited skills in towns like Burnley.
To end on a positive note, a relatively small and deprived town has produced a football club which looks like it might survive in the Premiership.