Yes campaign makes its final push for victory

Ed Miliband and Nick Clegg last night made last-ditch pleas to the public to defy David Cameron and the pollsters by supporting a historic change to the voting system in tomorrow's referendum.

As the Yes and No camps held their final rallies of a bitter and hard-fought campaign, the Labour and Liberal Democrat leaders both insisted that the pro-reform lobby could yet pull off a surprise victory.

A ComRes survey for The Independent suggests that opposition to a switch to the alternative vote (AV) has hardened. It found that 66 per cent of people who are absolutely certain to vote want to preserve the current first-past-the-post system, with 34 per cent backing AV. Although 15 per cent of those who will vote have not yet decided which side to support, the No camp still enjoys a big lead – of 56 to 29 per cent – when these "don't knows" are taken into account.

Despite the poll blow, the Yes organisation insisted there was still a prospect the public would use the once-in-a-generation opportunity to back reform of the voting system in Britain's first nationwide referendum since 1975. Mr Clegg said: "All the progressive forces in British politics have come together to campaign for a Yes vote – the Liberal Democrats, the leadership of the Labour Party, the Greens, the SNP and Plaid Cymru. We have a once-in-a-generation chance to make our democracy better – we must take it."

Both camps put on a show of support by staging cross-party rallies. Last night Ed Miliband joined the former home secretary Alan Johnson and the former Liberal Democrat leader Lord Ashdown on a Yes platform. The Labour leader said: "If you believe that this is a genuinely progressive country, then we need an electoral system that can reflect the views of the electorate and give expression to the anti-Conservative majority. AV would do that. That is why I am proud to say Yes to better politics and Yes to a system which reflects the progressive majority in Britain."

The ComRes survey suggests that Mr Cameron's high-profile intervention in the campaign has mobilised Conservative supporters against change.

Labour supporters, who are seen as crucial by both camps, oppose AV by a margin of 60 to 40 per cent. Conservative supporters reject AV by 88 to 12 per cent, while Liberal Democrat supporters back AV by 72 to 28 per cent.

The Yes camp hopes for a last-minute change of heart among Labour supporters. Neal Lawson, chair of the democratic left group Compass, warned that Mr Brown's administration "could well have been the last Labour government". He said: "Labour supporters have just 24 hours to wake up and start to change the future of politics. The outcome of this referendum is in Labour's hands."

In the No movement's rally, it fielded the Foreign Secretary, William Hague, the Home Secretary, Theresa May, the shadow Health Secretary, John Healey, the Labour peer Lord Boateng, the crossbench peer Lord Owen and the Olympic rower James Cracknell.

According to ComRes, Labour's lead over the Conservatives has dropped to three points. Labour is on 37 per cent (down two points since a survey for The Independent on Sunday published on 17 April), the Tories on 34 per cent (down one point), the Liberal Democrats on 15 per cent (up five points) and other parties on 14 per cent (down two).

ComRes telephoned a random sample of 1,033 adults across the United Kingdom on 28 April to 1 May 2011 (voting intention based on 1,003 GB adults). Data were weighted to be representative of all adults and by past vote recall. The AV result is predicated on those who said they were "absolutely certain" to vote on 5 May. ComRes is a member of the British Polling Council and abides by its rules. Full tables at www.comres.co.uk.