As we saw with Nick Griffin on Question Time, providing freedom of speech allows individuals and groups to represent themselves and show their true colours; it also allows the public to draw their own conclusions. People, as they say, can be their own worst enemies. The best course of action would be to ignore the group in question, show the classic British stiff upper lip, strength of character and resolve. By reacting and providing media coverage, we make the group seem more influential and powerful than they really are; this is typically the goal of such an action.
I hadn't really given this much thought until I spotted a few of my connections on Facebook (I will not use the term friends in this instance, and may have to review the policy) had joined various Facebook groups organised to protest against the proposed march. I also got pinged a link by Morcs which started me reading the content of some of these groups. I can only say that what I found was deeply depressing and saddening; the majority of comments are racist and xenophobic. They also feature a startlingly poor standard of literacy and there is a worrying amount of claimed support for the BNP and EDL.
To save your eyes, I'll summarise the common themes. For your sanity I've corrected the spelling and grammar rather than quote verbatim:
"I'm not racist but
"The BNP aren't racist, they just tell it like it is"
"If they want to march, they can go and march in
"If you don't like it, go back home" (What? To London/Bristol/Winchester/
"I'm pure white British and proud" (Umm... 18,000 years ago your genetics started out in Western Asia, or more recently you could be Roman, or Norse?)
"They should all be rounded up all be rounded up an
"If they don't like our laws they can stop taking all our benefits and jobs and go back where they came from"
"I'm not racist, my friend is Muslim/Pakistani/etc, but
I don't think I have the heart for further summary, if you can bear it you can read for yourself here, or specific examples here and here (don't say I didn't warn you).
The overriding message seems to be that the majority of responders on these groups (the largest has over 600k members) think that if you're not white, you're not British and that if you're not British you should be shipped out of the country. Is this really what the majority of modern Brits think? And people complain that we no longer have any national pride, I for one can't see much to be proud of right now.