If the Lib Dems do well in this election, it will be down to the madness of crowds

It is now generally accepted that David Cameron made a colossal blunder in agreeing to the televised debates. Had last Thursday’s debate not taken place, the Conservatives would still have a comfortable lead over the other two main parties, on track for a small overall majority.

Yet among the commentariat — even those in the blue camp — the consensus is that the debates are good for politics.