UKIP got a big vote in the last European elections with lots of protest votes but are widely seen as a one issue party and so not really a factor on the national level.
It's an oversimplified analysis to say that UKIP cost the Conservatives x number of seats. People who vote UKIP are by definition rejecting the Conservative policy on Europe to such an extent that they would rather register a protest vote for a candidate with no chance of winning and risk allowing a more left-wing candidate in than vote Tory. It's a stretch to imagine that all of those people vote Tory if UKIP isn't there.
Ah, much like our Buchananite crowd, or whomever they choose to vote for in our Presidential elections. The permanently disaffected third party crowd.