Labour today comes the closest yet to suggesting that its supporters vote tactically in constituencies where the main battle is between the Liberal Democrats and the Conservatives.
In an interview with The Independent, the cabinet minister Peter Hain urged people to "vote with their heads, not their hearts" as he issued a last-minute appeal to supporters of other parties to rally behind Labour "for the only time in their life" to stop David Cameron becoming Prime Minister in Thursday's election.
"I support every Labour candidate and the Liberal Democrat leadership supports every Liberal Democrat candidate. But voters are intelligent and they know what the real fight is in their own constituency. They will draw their own conclusions," he said.
Ed Balls, the Schools Secretary, makes a similar plea in the New Statesman magazine, saying: "I always want a Labour candidate to win, but I recognise there's an issue in places like North Norfolk, where my family live, where Norman Lamb [the Liberal Democrat candidate] is fighting the Tories, who are in second place. And I want to keep the Tories out."
In his interview Mr Hain, the Secretary of State for Wales, also offers the Liberal Democrats the prospect of a four-year "partnership government" so they could be sure Labour would not call a second election at a time to maximise its own chances.
"If there is a partnership government, it would be an agreed programme and an agreed timescale," he said. "As there is a commitment to fixed-term, four-year parliaments, it would be logical to form a partnership government on the basis of a fixed term. So the senior partner could not pull the rug on any party with whom they were in partnership."
Labour's moves will be seized on by the Tories as a sign of its desperation, and were rebuffed by Mr Clegg, who told people: "Vote with your heart, vote with your instincts."
The latest ComRes poll for The Independent and ITV News shows the Tory lead down two points to eight points since the weekend. The Tories are on 37 per cent (down one point), Labour on 29 per cent (up one), the Liberal Democrats 26 per cent (up one), and other parties 8 per cent (down one). These figures would leave Mr Cameron 32 seats short of an overall majority.
Mr Clegg's personal ratings are falling. The number who think he "deserves a chance to run the country" has dropped from 51 to 42 per cent since 21 April, while Mr Cameron has risen two points to 50 per cent, with Mr Brown on 32 per cent (down one point). Mr Cameron's support appears to be hardening. One in four Labour supporters (24 per cent) and a third (33 per cent) of Liberal Democrat voters believe he deserves a chance.
Some 48 per cent of the population believe that Mr Cameron would make a good prime minister (up four points), with Mr Clegg scoring 42 per cent (down three) and Mr Brown 30 per cent (unchanged). Mr Clegg is ahead when people are asked whether the leaders "understand the problems faced by people like me". He scores 49 per cent, Mr Cameron 42 per cent and Mr Brown 41 per cent.
When asked if they have a good idea of what the leaders stand for, 68 per cent say that statement applies to Mr Brown, 67 per cent to Mr Cameron and 61 per cent to Mr Clegg.
In his interview, Mr Hain said he was not asking voters to endorse everything Labour has done or its manifesto. "This is not a referendum on our record; it is a choice between stopping the Tories ruining Britain and destroying a once-in-a generation opportunity for political reform to the voting system – a democratically elected House of Lords."
His message was: "If you vote Labour just once in your life, now is the time to do it, especially in the key Conservative-Labour marginals. A huge majority of the electorate does not want a Conservative government; that is why the Tories are not romping home in this election. I know many of these people are not natural Labour supporters, but are they willing to pay the price of a Conservative government?"
Baroness (Betty) Boothroyd, the former Commons Speaker, announced her conversion to electoral reform, condemning the first-past-the-post system as unfair, fostering disillusion and inviting anarchy. She said: "The 21st century has no place for a system in which millions of voters are ignored because our elections are stacked against them."
Mr Cameron will campaign through the night tonight, meeting people such as fishermen, bakers and florists working through the early hours, and may feature on all-night radio programmes. Mr Brown has a gruelling schedule in English and Welsh marginals before heading to his Scottish constituency.
Last night the Financial Times came out in support of the Conservatives, having backed Labour in the last four general elections.
ComRes telephoned a random sample of 1,024 GB adults on 1-2 May 2010. Data were weighted to be representative of all GB adults. ComRes is a member of the British Polling Council and abides by its rules. Full data at www.comres.co.uk
In the South-west, this election is a two-horse race
The narrow, meandering road cutting through the idyllic Somerset village of Rode tells the story of the election battle in the South-west. Drivers heading to the local post office first pass a house sporting a banner for David Heath, the Liberal Democrat MP for the Somerton and Frome constituency.
Just a few doors down on the opposite side of the street, a sign asking voters to back Annunziata Rees-Mogg, the candidate hoping to win the seat for the Tories, stands proudly in a rival garden.
It is a two-way battle replicated in many seats across the region. While Labour has some inner-city strongholds, it is not a force in the way it is across other areas of Britain. Even in rare South-west seats which have been three-way marginals in the past, the fight in this campaign now appears to be between the Tories and Liberal Democrats. Ever since last summer, when Eric Pickles, the Tory chairman, hung around Westminster to finalise his party's election strategy, he saw the region as key to delivering a decisive Tory victory.
With many of the Liberal Democrat MPs defending very small majorities, it seemed as if the Tories would make inroads into Nick Clegg's heartlands. The likes of Jeremy Browne, who won the Taunton Deane seat by just 573 votes, and Chris Huhne, defending a 568 majority in Eastleigh, looked doomed. The leadership debates have delivered a boom in support for the Liberal Democrats since then, but there are local factors at play that mean Mr Clegg's MPs may need the support of Labour voters to survive.
Having won control of many councils, the party has been attacked as the establishment, performing poorly at the last local elections. The Tories are still fighting hard, with David Cameron visiting the region over the weekend.