Until guilt has been proven, innocence must be pressumed, regardless.

It's not exactly Sherlock Holmes. Griffin claims that the 1976 law doesn't apply to the BNP because it's a "membership association" as defined in clause 26 of the legislation. However, what clause 26 says is that the exemption applies

if the main object of the association is to enable the benefits of membership (whatever they may be) to be enjoyed by persons of a particular racial group defined otherwise than by reference to colour

In other words, to claim exemption Griffin has got to argue that the main object of the BNP is to give its members the benefits of membership - not to give other people the (debatable) benefits of being governed by them.

To go back to my shoplifting example, if I see someone cut off a security tag and walk out without paying, I don't need to await the outcome of a court case to conclude that that person's broken the law - and if they told me it was OK because they belonged to the British Shoplifting Party, I'd conclude that their party was working on the wrong side of the law. The evidence that the BNP, collectively, is on the wrong side of race relations law is really hard to ignore.