I'm surprised they even believed for one second that calling Islam an evil and vicious religion would be enough to get him convicted.
There are double politically correct standards too, with Islamic radicals calling for beheadings and murders whenever their religion is criticised (like the disgraceful reaction to the Danish cartoons) yet little action being taken against such violent statements and slogans.
One of the basic ideas of law is that you never go after someone unless you are really confident that you have enough to secure conviction. By bringing this moron Griffin up on weak charges then finding him not guilty, all that was accomplished is that the Government has given the BNP further publicity and a platform for Griffin to vocalise an image of defiance.
The way for the BNP to be dealt with is quite simple, but it requires rational thought, which is something that is often an alien concept to politicians. You deal with them in the following ways:
1- Address legitimate problems.
Not all the BNP supporters are brain-dead racists. The BNP do what bigots have always done. They exploit people who believe that the Government and the major parties have failed or abandoned them. When you have angry disgruntled people they are vunerable to being seduced by people who cater to their anger and offer them an extreme solution.
In parts of the UK the population is divided greatly with ghettos of so-called "cultures". The multi-cultural model has failed because the Government has allowed a situation to develop where many of these "cultures" do not feel the slightest bit "British" or "European" or even "Western". You can see this when you receive a letter from your local council and you turn it over to see the same message written in seventeen different languages. If the Government addresses real problems like housing, crime, urban decay, immigration, poor education facilities etc...it will remove the means that the BNP use to appeal to the disaffected. Of course, this means that the Government will have to do what Governments and politicians often don't do. IE: solving social problems and actually governing intelligently.
2- Equal Standards.
Like I said above, the Government choose to prosecute the BNP leader because of supposed "racial hatred". This is also another means that the BNP use to gain support. They can say "Look, the Government forces came after us for criticising Islam but didn't go after these guys who wanted to cut people's heads off" and they'd be right in a sense. If you try to be too politically correct over it and only go after the white guys but not the Islamic guys, you give the extremists another thing to exploit. The recent convictions of the three

3- Bring Them Into The Light.
One of the best ways to deal with extremism is to bring it out into the open. Instead of trying to marginalise the BNP and their supporters by pretending they don't exist, you give them a forum to speak their absurd views and you get experts who can soundly debunk them and show them to be the hateful idiots that they are. This can only be done in accordance with 1) first dealing with the legitimate issues they are exploiting which I mentioned earlier and 2) having experts to debunk them who won't simply spout out Government spin and the typical political habit of dodging issues and avoiding questions. If you have a Government apologist debating with a BNP member for example, they will lose the casual viewer/voter who are quite frankly sick and tired of politicians not providing answers to serious issues.