Formed from foreign ideology, rejecting historic British values of the basic equality of all people, engagement with the world, and political change through evolution, not revolution, the BNP is about as anti-British as you can get.
If they were British then why do they keep banging on about the Holocaust? The reason is simple, if your ideology is based on far-right philosophers from the continent then you have to attack the greatest single argument against them. So the BNP feed the Holocaust denial industry, because intellectually they have to. If your beliefs lead to extermination camps then they must be wrong. So, try and pretend the extermination camps never happened and that the Allies were just as bad. Imagine that, a political party with 'British' in its title that believes in moral equivalence among the participants of World War 2.
But this is why the BNP are fundamentally anti-British: