How important is Scotland in deciding this election?

Scotland has traditionally leaned further to the left than England and, in trying to hang on to votes in what were once Labour’s heartlands, such as Glasgow and Lanarkshire, the SNP have been keen to highlight tensions within the Labour movement over a range of issues, including Gaza, immigration, welfare and public spending.

At the same time Mr Swinney keeps trying to turn the attention back to independence, presenting it as an escape route from what the SNP call broken Brexit Britain — a nation of entrenched low growth, low productivity and high inequality.

Sir John Curtice says the reason for Mr Swinney adopting this tactic is clear: “While support for the SNP has fallen sharply over the last year, support for independence has not.

The SNP, he says, has lost “a significant proportion” of independence supporters to Labour, the Scottish Greens and Mr Salmond’s Alba Party.

Persuading those voters to return to the SNP represents “the SNP’s best hope of restoring its fortunes between now and 4 July,” adds Sir John.

Although there is no clear mechanism for Scotland to actually achieve independence at present, because both the Conservatives and Labour are intent on blocking a second referendum, some unionists nonetheless argue that the issue must be addressed.