The Institute for Public Policy Research has issued a report on the correlates of BNP membership and support (pdf).
Fascinatingly, they reckon that there is very little or no correlation between BNP support and key socio-economic indicators like GVA per capita, growth, unemployment, immigration, etc. It's as if a typical BNP supporter was, well, a case of free-floating extremism. (A dedicated swallower of fascism; an accident waiting to happen.)
Oddly enough, this replicates an earlier result.
The Nottingham University Politics blog has a more nuanced response, but I'm quite impressed by the fact that two analyses based on two different metrics of BNP support - votes in the IPPR study, membership in mine - converged on the same result.