It's all in the timing: Cameron's poll 'win'
Yougov say their internet poll on the debate last night was conducted between 9.27pm and 9.31pm.
This may explain why Yougov gave David Cameron a better rating than the other post-debate polls did last night. For Nick Clegg ended the debate with a very powerful closing speech, probably the best of the evening.
According to the BBC video system Clegg didn't start speaking until 9:29:18 and finished at 9:30:47.
So many of those polled by Yougov last night must have voted without seeing his final speech.