Regular readers of this blog will know that I rarely agree with David Cameron, but I can't help but concur with his line on the Lib Dems this morning:

He [Cameron] said the Lib Dems were in "complete muddle and confusion" as they had not spelt out what they would do if Labour won the most seats -- but comes second in terms of overall votes.

He's got a point, hasn't he? On Sunday, Clegg threw away months of hard work, having dodged and ducked questions about which party he would back ever since talk of a hung parliament went mainstream back in November. His careful formula was expressed on the BBC's Andrew Marr programme on 22 November 2009:

I start from a very simple first principle: it is not Gordon Brown or David Cameron or Nick Clegg who are kingmakers in British politics, it's the British people. Whichever party have the strongest mandate from the British people . . . have the first right to seek to try and govern, either on their own or with others.

Even though he was then repeatedly asked to define "mandate" -- votes or seats? -- Clegg stuck to this carefully worded formula right up until the start of this election campaign on 6 April. But Cleggmania seems to have gone to his head -- and he threw away all the hard work he'd put into evading and dodging the "What do you mean by a mandate? Votes or seats?" question.

On yesterday's edition of Marr, elaborating on his statement in the Sunday Times, the Lib Dem leader said:

It seems to me that it's just preposterous, the idea that if a party comes third in terms of the number of votes, it still has the right to carry on squatting in No 10 and continue to lay claim to having the prime minister of the country.

. . . What I'm saying here is pointing at a very, very irrational possible outcome of our potty electoral system, which is that a party that has spectacularly lost the election . . . could nonetheless according to constitutional tradition and convention still lay claim to providing the prime minister of the country.

The genie is out of the bottle -- and Cameron is right to point it out. Once Clegg has said the Lib Dems won't back Labour if the latter comes third (but wins most seats), he has to explain whether they'd back Labour if it comes second (but wins most seats). Clegg's ducking and diving will no longer do.

So the Lib Dems do seem muddled and confused. Clegg's answer, says the Indie's Simon Carr:

. . . certainly surprised a senior member of the Liberal Democrat command I mentioned it to later. "Surely he said that he wouldn't support Gordon if Labour got fewer votes?" Nope, he wouldn't support the Labour Party. "I'll have to go and watch it," the Liberal Democrat said.

Maybe it was a mistake. Because then Marr asked what he, Clegg, would do if Labour changed the leader after the election. He didn't say: "I repeat, if the party lost the popular vote, I wouldn't keep it in office." He said instead: "Here we get into the 'what-if' territory that I find very difficult."

And he went back to earlier ideas of collaborating with the party that would deliver Liberal Democrat manifesto commitments. But he couldn't do that with Labour polling fewer votes than the Tories because he ruled it out.

There is another important point worth raising: why does Nick Clegg think Gordon Brown would automatically lose the right to remain in Downing Street if Labour came third? Why do the Lib Dems, who have for so long rightly argued for the need for a government to secure more than 50 per cent support from the electorate, now seem so obsessed with pluralities and not majorites, that is to say, with who is first, second or third, rather than with who can command majority support?

The fact is that if -- and, I admit, it remains a big "if" -- the Lib Dems decided to enter into a formal coalition with Labour on 7 May, then such a coalition government, with Brown in charge, would -- according to current polling -- command the support of more than half the electorate.

In fact, such a coalition would have a greater popular mandate, and reflect the votes of a higher proportion of voters, than any government since the Second World War. So why couldn't Brown then stay on in No 10?