Heya Stinky, I'm very suprised you didn't know that. The BNP and I think members of the National Front aren't allowed into the police force mostly because they are expected to treat everyone they meet with respect regardless of race or skin colour. Unfortunately, or fortunately - depending on your point of view, members of the BNP and the National Front generally don't treat someone of a darker skin tone with the same amount of respect they would give a white person. In other words: the police are supposed to be politically neutral and the top brass don't trust the BNP. (They do have very strong views and are passionate about them.)
But you do highlight a very interesting double standard about how ultra-left winged folks are exempt from this ban. If members of the BNP are excluded against, why not the BNP's left wing counterpart. (If it has one.)
If you aren't willing to stand behind your troops, feel free to stand in front of them.
Lex iniusta non est lex