Looking at the result of the Henley by-election, the Tory share of the vote went up from 53.5% to 56.9%, the Lib Dem share also increased (from 26.0% to 27.8%), and the Labour vote collapsed from 6862 votes (14.7%) to 1066 (3.1%).
I interprete this as the public having an anti-Labour sentiment, but without any great enthusiasdm for the Tories or the Lib Dems. Cameron’s doing well not because of his own strengths but because Brown and Labour are doing badly.
In fact, the BNP got 1243 votes (3.6%), putting Labour into 4th place — Nick Griffin is more popular in Henley than Gordon Brown. It’s not surprising the BNP did well when you have senior Labour ministers like Harriet Harman apparently believing that racial discrimination against white people is OK. You might even conclude that Harman is a secret BNP mole.