I would agree to take a non-violent approach as it will draw attention to the fact that the BNP are around and maybe stir some feelings of an anti-leftist sentiment. We do not want the BNP to have any excuse for the BNP to gain support through sympathy, or through uniting the right-wing against us. At this moment in time we need to defeat them on an ideological basis. A time for violence may come eventually but it is not know. Use local organisations of the left as suggested, or stickers but don't give them an excuse to show us in a bad light.
p.s. Temper is a failing in all of us, don't worry about getting angry. Despite what I have said no one would blame you for smashing the fucking car's window.
"Ensanguining the skies,
How heavily it dies,
Into the west away.
Past touch and sight and sound,
Not further to be found,
How hopeless underground
Falls the remorseful day" A.E. Housman
I HATE the Chinese state, it does more damage to Leftism than Nazism and Fascism combined.