Like many other British people, I am concerned about the BNP. But I also think it's necessary to keep things in perspective.
While the BNP seems to be doing marginally better than in the past, their heyday was in the tense times of the early to mid-1980s; I even remember seeing police officers writing the party's initials from the inside of a condendation filled police bus window on the way to break up some rioting.
There does seem to be a correlation between economic turmoil, collective soulsearching and vulnerability to populists, as someone has already pointed out. However, at present we're far from the devastating economic collapse of 1930s Germany. In the case of the UK, not even the turmoil and far-reacning instability caused by an extremely painful change in economic model during the 1980s gave the BNP anything close to a majority political voice. While I do feel that people in the UK are increasingly frustrated with parts (only parts) of the political system, I don't think this reaches the desperate levels that populist parties require to rise to power. The credit crunch is definately biting hard, but people are still comfortable enough not to reach for desperate solutions. Also, if the BNP were to begin a sharp increase in popularity, I think the mainstream right would just coopt their ideas - and achieve Sarkozy's feat of totally destroying Jean Marie Le Pen's Front National in France.
None of the more radical (meaning end of spectrum; not violent) political movements of the 20th century ever took root in the UK. This was due to lack of large-scale economic upsets and the fact than on the whole, people have been generally satisfied with the status quo. While this could change, I tend to think that there's something in people's general mindset and sense of humour that just doesn't take radical ideologies seriously as viable political options. We wouldn't want to cause a scene now, would we?
Lastly, it's definately true that there's been a palpable shift to the right in Europe since the 1980s. I would suggest that this has little to do with immigration (which started much earlier - while people generally voted left), and everything to do with a shift in economic policy toward a shrunken state and free-market economics. This has fundamentally changed the society we live in and people themselves. From yuppies to niche marketing, people are now much more focused on themselves and their identities as a route to change than on grand political ideologies, as many concerned with change were in the early and mid-20th century. The collapse of the left and the merging of political ideologies into different brands of the same free-market, social-democrat ideology means that piecemeal (but nonetheless important) issues such as immigration, the veil, gay rights, fox hunting take centre political stage at different times - rather than large debates about structural issues. In my view, we really need to get back to talking about these large-scale structural issues that concern us all: perhaps this has already started with the environment and the world economic system. THIS is the way to combat the BNP, because the BNP has no position on these big issues - their people are just not skilled enough to deal with them. Stop distracting us with immigration and let's talk about why there is immigration: this discussion must lead not to more aid so "they" don't come "here", but to resolving structural economic inequality at global level.
Sorry about the rant. Once you get me going, there's no stopping me.
Goodnight!