Leading article: This vote is too important to be distorted by party politics

A few weeks ago, there were fears that the referendum on electoral reform would come and go without anyone except the cognoscenti on either side really noticing. Such was the apparent public apathy towards a change in the voting system. No one can say that now. The Liberal Democrat grandee, Lord Ashdown, weighed into the debate yesterday, to accuse Conservative opponents of the alternative vote of "scare-mongering" to secure victory for a No vote. And he accused the Chancellor, George Osborne, of resorting to "cynical smears".

Within hours, the Conservative leader, David Cameron, had piped up in defence of Mr Osborne, saying he had been right to speak about the way the Yes campaign was funded, but calling for a reasonable argument on both sides. The impression was left of Mr Cameron and Mr Osborne playing "good cop, bad cop" in their efforts to persuade voters to keep the first-past-the-post system.

After all the heat generated over the past week, the arguments for AV, presented in The Independent today by the Labour leader, Ed Miliband, seem cool, calm and collected. Mr Miliband focuses on the capacity that a switch to AV would have to improve the public perception of politics, foster the engagement of voters and make politicians more accountable. He also rejects utterly the spurious arguments of the No campaign, that AV would somehow benefit extremist parties.

But Mr Miliband also makes another point, which is at root a call for grown-up politics. First-past-the-post, he argues, entrenches a way of doing things that encourages parties to go into elections professing hatred for each other. Under AV, he says, candidates will need to be more honest about points of agreement.

Now there should be no mystery about why Mr Miliband is talking up the virtues of cross-party consensus and a new style of politics. This is a broad hint that he intends to play a long game, looking to a time when he, rather than Mr Cameron, might be the party leader in a position to make that "big, open and comprehensive offer" to the Liberal Democrats. His decision to share a platform today with the Business Secretary, Vince Cable, who only last week cemented his claim to be his party's senior in-house dissident – by attacking Mr Cameron's speech on immigration – demonstrates how concerned Mr Miliband is to keep channels of communications open.

This was the indirect message. But the direct and immediate message reflects Mr Miliband's fear that the referendum campaign is being fought increasingly along party lines. This is not a danger that was identified early on. It was assumed then that, with Conservative and Labour MPs both split on AV and each fielding forceful advocates on either side, the referendum campaign would be fought on the issue of electoral reform and on that alone.

As the No campaign has upped the rhetoric, however, it seems to be becoming more closely identified with the Conservative Party, just as the Liberal Democrats are, as a party, identified with AV. This, Mr Miliband argues, poses the risk that some on the right might vote No in the referendum mainly as a protest against the Conservatives' coalition with the Liberal Democrats, while some on the left might also vote No to "punish" Nick Clegg for his perceived sins: helping the Conservatives into power and his U-turn on university tuition fees.

Mr Miliband is right to point to this danger, which is heightened by the fact that many areas are holding council elections on the same day. It means that the Yes campaign must not only hammer home the merits of its arguments, but underline the distinction between an election and this referendum – a once-in-a-generation chance to change our electoral system for the better.