It's not only the UK that has a 'problem' with creeping Americanization, the biggest private employer in France I believe is now McDonalds.
But this is the result of global capitalism, something the Islamic community is actually against and the British invented!
Global capitalism has been aided and abetted by improvements in transport and communications, starting with shipping and the railways over a century ago.
For example, the low cost airlines have increased people moving to southern Spain, and now has 2 million Brits living there - much to the annoyance of the Spanish. Especially as the Birts tend to live in little 'like-minded' enclaves, and don't give a stuff about Spanish culture.
It's all very well saying 'pull up the draw bridge', but that has to work both ways. Are they organising a boycott of the airlines (or Eurostar for that matter) to stop all this travel that is diluting culture? No, they are picking on, in some cases, the most disadvantaged in society who have moved here, like Brits who have moved abroad, to better their lives.
How can the BNP say with a straight face, we want to stop people coming here, but don't mind British people invading other nations? Which, incidentally they have been doing for centuries, and especially in the last 20 years in terms of moving for jobs and second homes. Indeed, along with the USA, there is no nation on earth that has culturally and economically interfered with other races and countries. Britain probably stands alone in a particular sort of invasive policy to other countries. Look at the empire (which did have positive aspects too), but at the height of this country, which was somewhere around the first world war, we ran more parts of the planet than any other country has done before and since. But the truth is, UK influence has declined ever since, and was certainly overtaken by the USA in the 1950s and 1960s.
The internet and media is another cause of the dilution of culture, how many people now go around saying 'math' and 'vacation', because of the sort of media their consume. How many people wear jeans, when in the 1950s you were considered very poor if you did so, but US rock and roll culture made it fashionable.
So in short, if we were to have a sensible debate, what the BNP want is an end to global neo-liberal capitalism (which actually they do), they want restriction on travel (in effect) and a considerable 're-culturisation', which I really doubt many of its members would accept as it would mean a considerable adjustment to just about everything they do -they certainly need to learn tolerance, respect and manners for a start.
For example, the BNP talk about the destruction of community. Well actually that has more to do with planning (urban planning has moved to sprawl instead of tighter growth, typically seen before the 60s) and again market forces and technology, the way the indigenous people live their lives, driving to diffuse places of work, instead of all walking round the corner to the factory or office or riding on the tram like people used to, socialise in the pub instead of watching TV and especially instead of actually wanting to live their lives separately, or the sort of relationships they have, and screwing what they can out of things (by say the compensation culture) instead of working together through mutuals and friendly societies and so on.
They complain about crime, but one downside of capitalism is it produces losers, and the rich tend to get richer, which causes resentment. This is one of the key drivers, along with lifestyle choices like drugs and excessive alcohol.
There is no person more enthusiastic about the positive aspects of Britishness than me, but if you look at the real issues as a whole, it is much more complex than kicking out a few black people, those sorts of policies only appeal to the ignorant. There might be a case for controlling some of the excessive immigration in some areas, even serious political parties agree with that. I think there is certainly a case for adjusting some of the economic systems to control greed, environmental problems and putting in something that doesn't destroy heritage and tradition, not just here but elsewhere. But having a racist charter is just putting up barriers, when if anything those barriers should be coming down, and is the wrong way to go. The BNP would do far better as the party which celebrates British values, culture and design, but maintaining that tolerance which actually is a hallmark of the country as much as some of the other things.