AP Photo

We all know that Gordon Brown and David Cameron made a huge blunder by agreeing, several months ago, to give equal billing to Nick Clegg in the nation's first-ever TV leaders' debates. The Liberal Democrats made the most of their disproportional representation. Our politics altered forever.

But Thursday's final episode proved that the three-part system of debates does tend to correct its own exaggerations. It is, after all, a test by the public, of who should become prime minister. It has been described as a job interview.