ABOUT half way through her interview with the BBC’s Andrew Neil on Sunday, the First Minister visibly relaxed and started bantering about the grand inquisitor’s age. Her command of detail and policy puts Theresa May to shame. If there’s a better studio performer in British politics, I don’t know who it is.

It’s a pity the SNP election campaign isn’t going so smoothly. A Survey Monkey opinion poll at the weekend suggested that the SNP is now down to 39 per cent, only 10 points ahead of the Tories, and stand to lose one-third of its seats. Survey Monkey is not one of the more respected polling organisations; nevertheless, in the absence of any other opinion polls this survey of 2,000 Scots is all we’ve got. And there’s no doubt that the SNP is going to lose seats in the election.

The SNP has been caught between the Tory revival in Scotland and the Labour revival in the UK. The party has had great difficulty finding something to say, apart from “it’s not about an independence referendum”. Unfortunately, this election has been all about a referendum, or rather the reaction against it. There is a lot of anger on the doorsteps, to which most SNP activists, in their social media bubbles, aren’t exposed.

The SNP is still on course for a significant victory and today’s manifesto launch in Perth should help move the dial. But we live in an age of extraordinary political volatility, as Theresa May has just discovered to her cost. Nor is it enough just to say that only the SNP can stand up to the Tories in Westminster. Jeremy Corbyn seems to be standing up rather well at the moment, and the Labour manifesto is an attractive document that offers a genuine alternative to Tory austerity. Today’s SNP launch will struggle to match it.

Ms Sturgeon is expected for call for a 50p tax band, even though she’s rejected one in Scotland – an anomaly not easily explained. She also appears to have disowned Labour’s plan to increase corporation tax on similar grounds that it may not generate more revenue. But the SNP can’t win by joining the race to the bottom on tax.

Restoring corporate taxation to 26 per cent only takes it back to the level pre-2010, and is around the average in OECD countries. Ordinary voters are paying more than 26 per cent if you include national insurance. At a time of monstrous inequality, it is right to ask the wealthy, and the corporate sector, to pay their share.

The SNP is expected to call for £118 billion in public investment – a headline figure which sounds rather less than the £250bn Labour is proposing over the next decade. Ms Sturgeon is expected to lift the pay cap for nurses, and make further guarantees to public sector workers. But the majority of Scots are not employed by the state, and private sector employees are being savaged by wilting earnings and job insecurity.

The SNP will try to win over pensioners by attacking Theresa May’s abandonment of the triple lock and her scrapping of winter fuel allowance (the “dementia tax” not applying in Scotland). But the SNP seems only to be emulating Labour. Yes, Mr Corbyn has stolen many SNP policies, from abolishing tuition fees to scrapping hospital car parking charges, but you can’t win an election simply by saying imitation is the sincerest form of flattery. That sounds like complacency.

Cynically, the best thing for the SNP might be for the Tories to start attacking the First Minister’s talk of “progressive alliance” with Labour. The anti-Scottish sentiment we saw in the UK popular press worked well for the SNP in 2015 – remember hose Tory election posters of Alex Salmond picking the pockets of English voters. But the SNP can’t rely on nativism in social democratic Scotland. Nicola Sturgeon is the best political leader in the UK, but she needs something more to say than vote me.