They wouldn't have to split the Tory vote by much in this constituency.  The (current, Conservative) MP's majority is less than 3000, and he wouldn't have his seat but for a personal vote against the previous, deeply unpopular, Labour MP.

As ever, in the UK, a lot is about class.  The BNP is working class, and even unpleasant rags like the Daily Mail therefore feel obliged to rail against them. UKIP is a more Daily Mail demographic, the "acceptable" face of racism. But, yes, I'd say they're more a threat (in terms of vote transference) to the Tories than to Labour.