Agree with Roz. Convicted racists should not be allowed to stand.
And that should extend in principle to those convicted of any crime really.

To the original question, I'm sure it is illegal to post any offensive material.
But any out-and-out racist would have been quite disappointed by the BNP's leaflet - it could not be called offensive in any way.

The greater concern for me is that all the parties move even further to the right to partly cover the BNP's underlying agenda. Keep an eye on them too.