THERE was an odd whiff of the student debating society in the air today as David Cameron squared off against his deputy, the Liberal Democrat leader Nick Clegg, for a carefully choreographed start to the campaign over the Alternative Vote. With the filibustering over in the House of Lords, and a referendum on moving to this new voting system set for May 5th, the two party leaders had to set out why they dislike AV (in the case of the prime minister) or favour it (in the case of Mr Clegg).

But, like student tyros at a union society debate, there was a curious sense of formalised combat between chums, both of whom knew that their arguments consisted of a mixture of good points and try-ons. In parallel speeches and newspaper editorials, they were both exceedingly careful not to tear into each other. It was nothing like the atmosphere at Prime Minister's Questions, for example, which can often be genuinely venomous.

Mr Cameron's best argument for sticking with first-past-the-post?

It was when he said that with the AV system (in which voters rank candidates in order of preference, and votes for the least favoured candidates are redistributed until someone crosses the 50% line):

there could well be an occasion where we have a genuine second-choice government. If the last election was under AV, there would be the chance, right now, that Gordon Brown would still be Prime Minister

Leaving aside the rights and wrongs of AV (there will be time enough for chewing those over between now and May, believe you me), that line has real emotional resonance.

I have never forgotten the miserable atmosphere in Manchester last September when Ed Miliband won the Labour leadership after a leadership ballot conducted under the AV system. Part of that, of course, was down to the fact that the party members and MPs in Manchester had mostly voted for the elder Miliband brother, David, and resented the fact that Ed won on the back of union votes. But it was also the experience of watching the votes stacking up and being redistributed on a giant electronic screen, and seeing MiliD in the lead for the first three rounds, only to see him overtaken in the final round. So this is what AV feels like, I wrote at the time:

and it does not seem to feel so very good. Nobody here is threatening a coup. Nobody here in Manchester is suggesting that Ed Miliband did not win fair and square. But rather few here seem to feel exactly delighted, because so many of them voted for somebody else as their first choice

Mr Clegg's best point came when he framed his desire to see more weight given to third party votes with a concession. Yes first-past-the-post had worked well when two parties dominated British elections, he said, but those days were over:

The old system made sense when everyone voted either for the Conservative or Labour Party as they did 50 years ago. At the last election the two big parties mustered just shy of two-thirds of all votes, so you've got lots and lots of people whose voices simply aren't being heard. We need a system which reflects the variety of opinions which have developed in Britain over time

I think that it was smart of him to concede that there is a decisiveness to FPTP that is rather attractive, and to attack it now more in sorrow than in anger.

Mr Cameron's dodgiest argument?

I think that came when he argued that voters for fringe or extremist parties like the British National Party get extra votes compared to mainstream voters, because they can be almost sure that their second, third or even fourth preferences will be end up being added to the score of the eventual winner. Well, yes, that may happen, but something tells me that if a BNP voter's fourth preference results in a win for a Lib Dem candidate, that will not exactly be a cheering experience for the BNP voter. Also, in the system being proposed in Britain, nobody will be forced to fill in all the blanks on the form: voters will be allowed to place an X next to just one candidate. And something tells me that the angriest fringe party voters may do just that.

Mr Clegg's most spurious line?

Change in the way we do our politics come along once in a generation, whether it's the emancipation of women or giving the vote to millions of working people in this country

Yeah right. Last year he called AV a "miserable little compromise", and this year he is invoking Mrs Pankhurst.

When it comes to simply dreadful arguments, however, the official No campaign is making all the running. For reasons only they can know, they have decided to lead with the charge that a switch to AV would cost £250m, at a time when the public would rather be spending precious resources on schools-n'-hospitals or other worthy causes. Toby Young at the Telegraph blog site has a screen grab of a truly dismal poster showing a male model dressed up as a very unconvincing soldier, with the catchline:

He needs bulletproof vests NOT an alternative voting system. Say NO to spending £250m on AV. Our country can't afford it. No to AV

Mr Young makes the valid point that it is pretty depressing to obsess about the cost of a switch to AV (especially when the £250m number is pretty ropey, and involves adding up the cost of a referendum, voter education and the electronic voting machines that would supposedly be needed if Britain switched to AV) while ignoring the serious political arguments against such a voting system.

I have a still simpler objection. While I am as keen as the next man for British soldiers to be properly equipped, since when did we in Britain suggest that the cost of holding elections should be traded off against funding for the military? I imagine the cost of running a General Election under present rules is not nugatory. Is the No to AV camp suggesting we cannot afford proper democracy? Should we elect the next government by acclamation?

Still, clever of them to dream up a poster so dodgy that—should it fail to work in Britain—the No to AV camp can sell it to Colonel Muammar Qaddafi or the Egyptian military junta for use on the streets of Tripoli or Cairo, with only minimal alteration.