David Cameron is likely to “remain Prime Minister” because the predicted wipe-out of Labour in Scotland has reduced Ed Miliband’s chance of forming a government, the party's leader there has admitted.

A week from polling day, the extraordinary forecast by Jim Murphy suggests his party north of the border may have thrown in the towel in their efforts to halt the nationalist surge.

Mr Murphy made the uncharacteristically despondent forecast in an interview with STV after a new Ipsos-Mori poll for the broadcaster predicted Nicola Sturgeon’s SNP would win all of Scotland’s 59 seats.

The poll gave the SNP 54 per cent, increasing their lead over Labour to 34 points. Labour were down four to 20 per cent, just three above the Conservatives who recorded a five point jump.

The Liberal Democrats were up one to five, the Greens on two percent and Ukip on one.

Responding to the poll, Mr Murphy repeated the proxy argument that the Conservatives leader had focused on the SNP because his party in Scotland held no influence.

Describing the poll as “good” for the SNP but “fantastic” for Mr Cameron, he added: “David Cameron can’t beat the Labour Party here in Scotland, so someone else has to do it for him.”

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Mr Murphy then said: “The likelihood is David Cameron will remain Prime Minister, not because Scotland went out and voted for the Tory party but because Scotland voted against Labour for the SNP and reduced the chances of Labour forming the government.”

Although Mr Murphy added that a week was a “long time in politics” and he remained “determined to turn much of this round”, the timing of his prediction that Mr Cameron is likely to win a second term in Downing Street indicates the turn-around that he promised would happen when he became leader in December last year has failed to materialise.

Rather than lead his party out of trouble, the election campaign in Scotland – which has centred on warnings that a vote for the SNP would keep Mr Cameron in power - has been a reverse of the campaign in England and Wales where Mr Miliband’s reputation and standing has improved.

Reacting to Mr Murphy’s despondent prediction for 7 May, a Scottish Conservative spokesman said: “From this extraordinary admission, it seems Labour have finally faced up to the reality that they are in meltdown in Scotland.

“That’s not David Cameron’s fault, Labour’s demise is completely of their own doing.

“The chances of Ed Miliband getting to Downing Street are diminishing by the day, and Jim Murphy clearly agrees.”

In pictures: Experts' predictions for the General Election - 26/04/15 Show all 10 1 /10 In pictures: Experts' predictions for the General Election - 26/04/15 In pictures: Experts' predictions for the General Election - 26/04/15 Andrew Hawkins (ComRes) “This is an election of wild promises and political cross-dressing; so no differentiation, no breakthrough, no majority. The most likely outcome is Ed Miliband in No 10 because only he will be in a position to work with enough parties (that is, the SNP) to form a workable government.” Andrew Hawkins In pictures: Experts' predictions for the General Election - 26/04/15 Joe Twyman (YouGov) “As each day passes and the Conservatives fail to increase their vote share, the likelihood of Ed Miliband becoming PM (albeit still with a minority) grows. That’s due to the continued performance of the SNP in Scotland and former Lib Dem voters propping up Labour in England.” In pictures: Experts' predictions for the General Election - 26/04/15 Ben Page (Ipsos MORI) “A better week for Ed Miliband than for David Cameron – personal ratings improving, and the betting markets moved in his favour. The poll numbers have him ahead by a whisker which, combined with the electoral maths, makes him more likely to be able to form some kind of government on the raw numbers right now. However, Cameron will be hoping for a 1992 moment when ultimately voters can’t quite bring themselves to try someone else – and 38 per cent of voters still say they may change their mind.” In pictures: Experts' predictions for the General Election - 26/04/15 Rick Nye (Populus) “The Populus/Hanover Predictor has Ed Miliband ending up as Prime Minister in more than five out of six simulations we run.” In pictures: Experts' predictions for the General Election - 26/04/15 Nick Moon (GfK) “Tories most seats, SNP 45 or more, Ukip fewer than five: minority Labour government.” In pictures: Experts' predictions for the General Election - 26/04/15 Damian Lyons Lowe (Survation) “Ukip’s vote share is prone to be squeezed, benefiting the Conservatives, while the SNP’s onslaught on Labour continues. Based on three UK/Scotland polls, I am upgrading the Conservatives and the SNP, and downgrading Labour. Both the Lib Dems on 30 seats and Ukip on 5 to 10 remain unchanged.” In pictures: Experts' predictions for the General Election - 26/04/15 Michelle Harrison (TNS) “Still no change, but Nicola Sturgeon goes from strength to strength in Scotland. For me, who the biggest party is will hinge on the crucial marginals. But what ultimately wins – safety first, for the Tories, or Labour’s ‘get out the vote’ ground war?” In pictures: Experts' predictions for the General Election - 26/04/15 James Endersby (Opinium Research) “Our poll today shows a one-point Tory lead, statistically a tie. It’s going to be incredibly tight. Labour and the Tories would do well to be negotiating with the smaller parties behind the scenes. In the likely event of a hung parliament, we’ve been testing various combinations of coalition. Labour teaming up with the Lib Dems would be more popular than with the SNP, which in turn would be more popular than a Tory/UKIP scenario.” In pictures: Experts' predictions for the General Election - 26/04/15 Martin Boon (ICM) “Not much going on really, and no reason to change my mind. Tories by a couple of points. In pictures: Experts' predictions for the General Election - 26/04/15 Lord Ashcroft (Lord Ashcroft Polls) He refuses to make predictions. “My polls are snapshots, not predictions.” Rex

Adding to Labour’s woes is the Ipsos-Mori’s finding that 80 per cent are likely to vote on 7 May.

Although down on the record turn-out of 85 per cent in last September’s referendum, the figure is almost 16 higher than the turnout at the 2010 general election.

Labour have always believed that a low turnout, given the surge in SNP membership since the referendum, would help them in marginal seats.

Nicola Sturgeon, the SNP leader, said the polls made “wonderful reading” but said her party “will continue to take nothing for granted and campaign hard for every vote.”

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