I’m not so sure that UKIP will take more votes from the conservatives than from labour. That is the established wisdom, but established wisdom has not had a good track record recently, partly because it tends to be very London centric. 90% of Britons do not live in London. In the midlands and (especially) north of England UKIP is the firm contender against labour, and I believe they will win several seats there.
Its well known that UKIP has significant support across the country, but that is the problem, it is spread out across the country, and not concentrated enough in any one particular area. They will still be lucky if they get a single seat the the GE next year.