First you need to understand what strategy is and means, and too many political organisations, even the mainstream ones either don't know or have forgotten.
Strategy means looking at what you're facing and assessing which parts of your enemy's forces or ideology can be attacked and where so as to cause most damage, and then fighting your campaign, for which you need:
Tactics. Where strategy is your overarching plan, tactics are the plans you deploy to fight specific instances of contact. You tailor your tactics to the specifics.
So, in my opinion, strategy specifically aimed at insuring that the BNP have a hard or impossible job capitalising on any public sentiment leaning their way due to current structural and social issues, would centre around tackling those structural and social issues that can be dealt with at a grass-roots level, rebutting propaganda with fact "on the doorsteps", and keeping a momentum that doesn't just encompass a fortnightly or monthly protest in the town centre. We're talking hard work by the community for the community, to generate a result by the community for the community.
With regard to issues that can't be dealt with at community level, then concerted community pressure on local government can often do wonders once the local government establishment get over trying to "monster" you for daring to try to exercise actual community power rather than just a facsimile of it.
As for tactics, you deploy what you have to hand that bet fits the circumstances you encounter. If that means "shadowing" BNP canvassers and then canvassing wherever they canvass, then you do that. If it means digging into the background of your local BNP members, you do that and make sure that your local and regional media are aware. If it means "engineering" a confrontation, then you do that.