Politicians are opportunists, and someone like the BNP will take charge when the voters have had enough of the status quo.
The "far-right" BNP is vastly different than conservatives in the US. On immigration and race, they are like David Duke rather than Tom Tancredo. They do not seem to be fiscal conservatives either and basically appear to be National Socialists.
The problem with uber-liberalism is that as a reaction many normal people may react sharply to the right and get involved with such organizations.
Regardless, frequently charges of "incitement to racial hatred" keep them in court. However, those same laws stifle debate on Britian's vast problems.