The best bullwark against the BNP is a Labour party that reconnects with the Labour movement and the needs of the blue collar worker and a Tory party that is honest about the views of the rump of its supporters and doesn't pretend they are a blue shade of New Labour Lite.
It is also worth keeping in mind that the people with most to gain from a bump in BNP numbers are the far left. These are two sets of discredited parasites who feed off of eachother to the massive disinterest of the wider population. I take anything that the far left says about the far right and vice versa with a massive pinch of salt.