Several historians, including myself, comment here in the Guardian on the putative rise of the BNP. A remarkable unanimity prevails, although David Kynaston is a bit more pessimistic.

What is more striking is the collapse of the Labour vote, rather than the rise of the BNP. The latter only benefited from proportional representation; in a straight first past the post system they'd lose their deposits. I also think the UKIP vote simply represents the fact that these were European elections, where their issue bulks large. Again, in a real contest, their vote would migrate back to the Conservatives.