The Conservatives lead Labour by 36 per cent to 30 per cent in this week’s Ashcroft National Poll, conducted over the past weekend. The Tories are up two points since last week and Labour are unchanged. The Liberal Democrats are down a point at nine per cent, UKIP down two at 11 per cent, the Greens up three at seven per cent and the SNP down two at four per cent. The Conservatives have now led in six of the last eight rounds, and this week’s finding equals the highest the party has yet recorded in the ANP – though the figures are within the margin of error of a much closer result.

There has been little change in people’s preference of Prime Minister over the course of the campaign. I found just over half of voters saying either that they were satisfied with David Cameron (32 per cent) or that they were dissatisfied but preferred him to Ed Miliband (23 per cent). Just under three in ten (29 per cent) said they were dissatisfied and would rather see Miliband at Number Ten. Swing voters, who say they don’t know who they will vote for or that they may yet change their minds, were slightly more likely than average to prefer Cameron on balance.

One notable change since I last asked this question in February was the rise in the proportion of Labour voters who say they would prefer to see Miliband as PM. This will be partly down to potential Labour voters who find him an insurmountable barrier switching to another party, and partly to existing Labour voters thinking Miliband has had a good campaign. I also suspect that some who have decided to vote Labour despite their doubts about its leader are now telling themselves that he might not be so bad after all.

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This week’s focus groups took place in Glasgow, Paisley and Edinburgh, where people’s appetite for political debate seems undiminished in the six months since the independence referendum. “It ignited something in people… On my building site now no-one talks about football, it’s all politics”; “I look into things and listen a bit more. I would never have watched things like the debates before.” Though everyone thought this greater engagement was a good thing, the referendum had been a bitter experience for some, and a few had even lost friends: “People were shouting at each other in the office. It got quite unprofessional”; “It was testing for us because we were a divided household. We stayed in different houses on the day of the referendum because he was very strongly Yes; I stayed at home with the babies”; “My mother was a No voter and we fell out about it. But I had to go back eventually because she makes the best soup in the world.”

This election also felt different because, for the first time, people felt that Scotland was centre-stage. Whereas British politics had previously meant “anything south of Manchester”, people were now paying attention to the Scots. “The BBC news was live from Edinburgh for the SNP manifesto launch. I’ve never seen that before”.

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Most of our participants had voted Labour in 2010, and for as long as they could remember before that, as had their parents. Why were people switching to the SNP so ready to abandon the party that often described as being part of their heritage? The answer fell into one or more of three categories. First, that Labour (unlike the SNP) now seem politically indistinguishable from the Conservatives, at least to the many who said they wanted to support a socialist party: “I’ve been Labour like a stick of rock all my life but I’ve hit a wall with them. There is no discernible difference between them, the last fifteen years of government have been seamless. The SNP are the only ones pursuing a social agenda”; “Boris Johnson said Ed Miliband was dangerously left wing, but I see him as being centre-right”; “Labour sold out the working man to appease Tory swing voters”.

Second, that Scottish Labour are, to quote Johann Lamont (which several participants did) a “branch office” of the London party. This longstanding grumble had been sharply into focus by the prospect of a distinctively Scottish party having real influence in Westminster: “It’s the UK party that pulls the strings for the Labour party in Scotland. The referendum made people see that. Scotland is different”; “The SNP increasing in popularity makes the differences much more obvious. It highlights the fact that there is no Westminster SNP. They are the Scottish party.”

Third, that Labour had disappointed them during the referendum – not necessarily by supporting a No vote, but by (as some saw it) “backing the Tories” and conducting (as many saw it) a negative campaign: “They could have been ‘Labour for No’ and made a socialist case for a No vote, and let the Conservatives focus on their core voters. It seemed like they were pushing a homogenous establishment view rather than a Labour view”; “I voted Yes because I didn’t see a bright future for my kids under the status quo. If Labour had said things can be better, OK, but they said things are fine as they are”; “They were fear-mongering. They were telling pensioners they were going to lose their pensions.”

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Despite this, participants in all three locations spoke highly of their own Labour MPs. Douglas Alexander in Paisley was “an exceptionally good local MP. Very genuine and knowledgeable”. Mark Lazarowicz in Edinburgh was “a really honest guy, a man of the people like his predecessor”. Ian Davidson was “a very, very good local MP. When I’ve gone to him with something he’s always sorted it out. But he’s going to suffer for the sins of others.”

Most did not feel quite the same way about Jim Murphy, the Scottish Labour leader. This was largely a reflection of Scottish Labour’s overall brand, since several said they knew nothing about him until he took over. But those who had taken against him either accused him darkly of being a “Blairite”, which was an end to the matter as far as they were concerned, or thought he seemed “angry” and was “a shouter”: “He’s very negative. A merchant of doom”. One observation was that “he never looks as if he’s really that happy. It’s as if it’s torture for him, as though it’s a real chore”. Some did have a more positive view: “I think he genuinely cares, but they are just puppets for English Labour so they aren’t going to change anything.”

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The reaction in the groups to an upbeat Scottish Labour election broadcast setting out a series of plans and policies was accordingly rather sceptical. Some of this was familiar from the usual reaction in England: “I would love to believe it all but where’s the money coming from?”; “It’s funny how in the days coming up to the vote they miraculously manage to find millions and billions”. Others felt that with all parties producing lists of similar-sounding promises, it came down to a question of trust and credibility: “I like the sound of the policies but I just don’t believe they’d come through with it. I think the SNP would fight harder for it”; “X-thousand new houses, invest in this and that… It’s who you trust, and I trust Nicola Sturgeon more than any of the others”.

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So, Nicola Sturgeon. What do we think? “Fantastic. A lot of my family have never voted SNP but she appeals to them”; “She’s direct, she speaks from the heart”; “She seems more like an honest politician, if there is such a thing. You can relate to her.” Even many those who had liked and admired Alex Salmond thought Nicola had the edge on him: “He was a bruiser. He tended to flatten people and that’s what made him a Marmite figure. She tends to keep people on an even keel and carry folk with her”; “I got the impression that he wanted to be the King of Scotland, but I listen to her”.

People also felt she was making a good impression outside Scotland, which they thought was important: “It’s good that she’s getting out there. She won in a lot of the polls asking how they had done in the UK leaders’ debates”; “She was only known in Scotland but now it’s the whole of the UK. I think she comes across better to the UK as a whole than Salmond.” She also seemed a refreshing change from the established party leaders: “They are all public schoolboy-ish but she has this passion and fire”; “She took them all on and had the answers”.

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For those attracted to the SNP the biggest appeal was simply that they are “for Scotland”. At least as attractive for some was that the party had established itself to the left of Labour, a position into which it had evolved over time: “They used to be the Tartan Tories but they have turned right round in the last fifteen years”; “If you take independence out of the equation, the SNP are probably the same as Labour were 20 years ago. A party of the common people”; “They seem to have policies promoting more equality in society. A social conscience.”

If Scotland sent a large SNP contingent to Westminster, what would they be expected to achieve? The answer to this question was usually rather unspecific:

“I just feel our voice would be heard”. One recurring theme was that the SNP would be able to prevent Scotland being the “guinea pig” for unwelcome policies: “When you go back through history and see all the things that have been done to us, the poll tax and so on, that wouldn’t happen.” Some also hoped the SNP would win new powers for the Scottish Parliament and ensure the promises made by the UK government before the referendum were honoured to Scotland’s satisfaction.

Most SNP supporters agreed with the party’s stance on Trident (“put it in the Thames and see how many of them want to keep it then!”) But this was not a universal view (“with the state of the world, what else do we have?”), and most did not think the issue should be at the top of the policy agenda. People were more inclined to see the SNP’s aim of ending austerity as the more important priority. However, this pledge was greeted with a good deal less scepticism than the policies in the Labour broadcast. This was partly because ending austerity sounds like a change in approach, while concrete plans sound like things that have to be paid for. But some also felt the SNP’s track record at Holyrood gave them some credibility when it came to keeping promises: “The SNP have tackled a lot of stuff they said they would. Nicola Sturgeon was in charge of the NHS when we got free prescriptions.”

One thing nobody said the party should push for, and very few said they wanted, was an early second independence referendum. “We need to move on. I think everyone’s acknowledged that”; “I voted Yes but I don’t think you can keep having referendums until you get the answer you want. Apart from anything else, if we voted for independence people would then start saying they wanted a referendum to join the Union. It should be a generational thing, not every few years.”

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Potential SNP voters hoped and expected that the party would do a deal with Labour, supporting them on a vote-by-vote basis but not joining the government. Here they would be a positive influence: “It would be good for Labour, bring them back to their roots a bit more and swing them to the way they should be.”

The belief that the SNP would keep Labour honest and ensure Scotland got the best possible deal helped to counter the argument that a vote for the SNP would let the Tories in. Some said this hardly mattered anyway since there was nothing to choose between a government led by Labour or the Conservatives (“it’s just a different shade of shite”). When pushed these people usually admitted they would prefer Labour, but most did not accept that more SNP MPs made a Tory administration more likely. In fact, they reasoned, “if Labour and the SNP join up, it’s back in balance” – the left-wing bloc at Westminster would be as large as it would otherwise be, but with a bigger element looking out for Scotland.

If English voters took exception to a minority Labour government supported by the SNP, this would amount to “a wee taste of your own cake”, given how few Scots supported the current coalition. But there was a great deal of sympathy for the idea that MPs from Scottish constituencies should abstain on “English laws”. With a devolved parliament, voting on issues that did not affect Scotland would be “having two pies at the same time”. Scottish MPs should vote on matters that had even indirect implications for Scotland, but “we would be doing our English counterparts a disservice to push things through that didn’t affect us.”

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By no means all our participants were now planning to vote SNP. Some saw the party as divisive and untrustworthy and did not support the independence agenda. But those thinking of voting SNP for the first time often had reservations of their own. There were three main concerns. One was that the party would try to re-open the independence question, creating more uncertainty and fuelling a bitter debate that people wanted to think was settled for now: “They might try to lead us back into the independence thing, which would be quite frightening for a lot of people”; “Nationalism is not a very nice aspect of our society. You see some horrible versions of it and I would be worried about aligning myself to that”. Another, for some, was that there might really be something in the idea that by voting against Labour they would somehow be increasing the chances of another Conservative-led government.

The third was that the SNP at Westminster might over-reach and produce a reaction against Scottish demands, or otherwise fail to live up to the expectations it had created – either by being unable to exert the influence it hoped (and by no means all expected the SNP surge to materialise on the day), or by capitulating on important policies and becoming the new Lib Dems: “I hope it doesn’t divide and create anti-Scottish feeling”; “I’m worried they will get too big for their boots and let people down”; “Can they ever have enough MPs to make a difference?”; “It sounds good but are we going to have another Nick Clegg?”

For a few, there was an additional concern that many of the SNP candidates were young and inexperienced – especially in Paisley, where Douglas Alexander’s opponent, Mhairi Black, is aged 20: “If you had to go to your MP with a problem, which would you rather go to? I’m not against change but I think people might eat her for breakfast.” But most either took the opposite view (“I think it’s wonderful, refreshing. We need new ideas”; “I feel that they’re underdogs challenging all these old dinosaurs”) or that it hardly mattered either way (“The policies matter more than the candidates. They get whipped. They even get told what to ask at Prime Minister’s Questions!”)

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In these locations, most people were not giving any thought to the Conservatives. Even so, the groups had a very good opinion of Ruth Davidson, even though (they sympathised) she was “flogging a dead horse.” “In the debates she was strong. She gave as good as she got from Nicola Sturgeon and it was good to see the two of them”; “She excellent – genuine and conducts herself well. But I could never vote for her policies”; “The thing about her is that she’s true to what she believes in, so I respect her. Whereas with Jim Murphy, you never really know.”

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And so to the bigger question, namely who would play whom in Nicola Sturgeon: The Movie. The starring role, by common consent, would go to Dame Helen Mirren or, if the producers insisted on a Scot, Elaine C. Smith. Jim Murphy would be played by Peter Capaldi from The Thick Of It, or Jim Carrey, or (more encouragingly) Ewan McGregor. Sue Perkins or Rhona Cameron would play Ruth Davidson, and Scottish Lib Dem leader Willie Rennie would be portrayed by “a gentlemanly quiet person” like Geoffrey Palmer or Ashley from Emmerdale. David Cameron would be Hugh Grant or Colin Firth. What about Ed Miliband? “Woody Allen”. Ooft.

Visit LordAshcroftPolls.com for full details of Lord Ashcroft’s research and to sign up for news alerts. You can also follow him on Twitter: @LordAshcroft