Killing them with kindness
Not quite, let me explain
When I was a member of the Labour Party I noticed something about when the BNP stood at elections. NuLab went nuts, flyer after flyer denouncing the Hitlerite filth etc.
What happened? BNP votes increase, Tory votes increase.
A recent by-election saw the BNP top both NuLab and the Tories, coming second behind the LibDems despite a massive leafleting campaign by both the LibDems and NuLab and Searchlight campaigning in the area by the bus load.
As someone who is fascinate by the BNP as a social phenomenon I know they are scary out of government and incompetent when in it, merely backing Tory policies and ignoring their own election promises.
Surely the best way to combat the BNP is to drop the No to Nazi response and just point out that they are, regardless of ideology a shit party. Regardless of the bigger picture of anti-fascism and anti-racism, calling someone a Nazi when they're running to save a playing field down the road is overkill, makes the messenger seem immature, radical (in a bad way) and turns people off. NuLab lost voters becuase the BNP said they were a people's party, no nonsence etc. Calling them racists nutbars is not a response, the BNP is desperately grapping at a squeaky clean image, they've toned down their languague, policies etc. while anti-fascists play it like its the NF circa 1979. The average far-right voter usually isnt far-right and attacking it like they're part of an extreme clique is counter-productive.
It might not be the same and maybe even defeats the ideological point of being an anti-fascist but pointing out the BNP are a crap party not fit to govern, liars etc. is more likely in my eyes to put off many non-racists voters towards the BNP, and ultimately thats a key goal.
Kill them with kindness, beat them with their own record, not rhetoric

yeah you make a lot of very solid points that almost everybody here should agree on; however, whilst taking on board what you have said, there is a space to tackle the heart of the BNP which certainly does remain far right. What anarchists recognise is that the BNP are still a deadly enemy to egalitarian organising and autonomy whether they are Nazis or not.