just individual opinion: BNP in British Politics is nothing but a puppet of mainstream parties (either Labour or Tories)
When our politicians in Downing St or Whitehall need him, Griffin will appear on the BBC and shaking his ‘Facist’ flag in order to manipulate the public opinion and serve the need of Westerminster; once his job is done, Westernminster will only need move a finger to kick him out of the public sight. Temporary rise of BNP may cost some votes of Labour, but so does the Conservatives; if it is possible to use BNP as a lever to clean up the Tories influence over immigrantes issue, then it is worth to allow BNP to appear on the show.
Look on the serface of the story, BNP may looks like a rival to mainstream political parties; bt in certain sense, they all on the same side somehow. However, this is only one of the points of view after all, no need to argue about its correctiveness.