Conservative and BNP votes

There was some speculation before the election that the Conservative anti-immigrant platform might pick up votes from the BNP (one article mentioned that a similar approach in the past more or less wiped out the old National Front). I've no feel for the extent to which this actually happened or not, but something I did notice was that in Dewsbury Labour and the Conservatives both had Muslim candidates (the Labour one a member of the CRE too), and the Conservatives lost, by a smaller margin than the BNP vote in that constituency.

It seems fairly obvious that in that case the Conservatives weren't going to pick up BNP votes (and would surely have known this), whatever the case may have been elsewhere; what I'm wondering is how much they suspected in advance that it might actually cost them the seat.