Which it would be, although admittedly somewhat poetic justice. They're a registered political party who get votes. Those voters have a right to be represented. Whether you or I like them or not is irrelevant to that point. As long as the party (and not individual members) has been shown not to have acted illegally, the democratic process requires them to be present at some point.
Discriminating against the BNP on the grounds we don't like them simply gives them a legitimate grievance to air and strengthens their hand with people who believe they have been marginalised in modern society.
There is only one way to beat the BNP and it's the exact opposite of that. Get them on telly and show to the entire country what a bunch of knuckle dragging idiots they are. The whole thing with 'denying them the oxygen of publicity' backfired badly on Thatcher's government re: the IRA and it would backfire on anyone who tried it now.
Jon