The issue is not whether Nick Griffin’s appearance on question time wins the BNP more recruits or not. The key point is whether Britain is a democracy.
British people have a right to hear the representatives and spokespeople from political parties which win election mandates and/or have a significant following. It cannot be for the BBC (and it would be wrong for Parliament) to impose censorship.
The real horror is that in New Labour’s Britain, fascists can win 6% of the vote and two Euro seats, not that such relative success gives the BNP a right to be heard on Question Time.