The Tories can’t discredit the allure of a Labour-SNP pact this time – Brexit has made Scottish independence far too attractive

Warning about a ‘coalition of chaos’ would look pretty rich to voters after the catastrophe of Conservative rule since 2016, and that includes the ‘regressive alliance’ with the Democratic Unionist Party

As I interviewed Ed Miliband on his 2015 election battle bus, his exasperated aides frantically tried to persuade the BBC not to go big for a fourth day running on the prospect of a minority Labour government being propped up by the Scottish National Party.

“How damaging is it?” the then Labour leader asked me. “Bad,” I replied. He wasn’t convinced. But the Tories’ repeated warnings of a “coalition of chaos” if Miliband became prime minister in a hung parliament undoubtedly damaged Labour’s prospects.

It seems history is repeating itself. John McDonnell, the shadow chancellor, said last night a Labour government would not block the Scottish parliament’s call for a second referendum on independence.

He even adopted SNP language by describing Westminster as the “English parliament”. His remarks at the Edinburgh Festival Fringe contradict Dick Leonard, the Scottish Labour leader, and the party’s 2017 election manifesto. They came a day after Nicola Sturgeon, the SNP first minister, raised the prospect of a “progressive alliance” with Labour to keep the Tories out.

What’s going on? As in 2015, Labour can’t admit it, but knows it will be difficult to win an overall majority. Although he didn’t need to say it in public, perhaps McDonnell was preparing the ground for a post-election Lab-SNP deal – not a coalition, but a pact in which the SNP supported Labour in key votes in return for an independence referendum. If Brexit had not happened by then, their common agenda could include a Final Say referendum.

Inevitably, the Tories are reprising their 2015 attack, with their chairman James Cleverly warning: “This Sturgeon-Corbyn alliance would be a nightmare prospect for Britain.”

In 2015, the Tories hoovered up seats in the southwest held by their Liberal Democrat coalition “partners” in a below the radar campaign, claiming a Lab-SNP pact would see government money switched from the region to Scotland. No doubt Team Boris will soon warn that the billions he would spend on transport projects in the north of England would be diverted to Scotland. It could boost his campaign to target 2016 Leave-voting seats held by Labour.

Yet the Tories should not assume they have a magic bullet. A lot has changed since 2015. Warning about a “coalition of chaos” would look pretty rich to some voters after the chaos of Tory rule since 2016, including a “regressive alliance” with the Democratic Unionist Party and a £1bn bung for Northern Ireland to seal the deal.

Brexit has dramatically changed the dynamics of the Scottish question. A poll taken after Johnson’s visit to Scotland last week found that 52 per cent of Scots would vote for independence, with 48 per cent against.

Some 56 per cent of 2016 Remainers want a referendum in the next two years and 59 per cent would support independence. Scotland voted to Remain in 2016, so it is hardly surprising that Johnson’s 100mph drive towards the no-deal cliff edge has fuelled support for independence. It’s not great news for the Scottish Tories, whose gains in 2017 allowed May to remain in power. Ruth Davidson, the Scottish Tory leader, has warned Johnson against no deal and sent Downing Street the Scottish media coverage of this week’s poll. Of course, opinion could switch back if the UK leaves the EU. Would Scotland risk losing its single market with the rest of the UK for one with the EU? The messy Brexit process might not be a good advert for divorce.

But the apparent rise in support for independence is another reminder of the forces unleashed by Brexit, particularly a no-deal one. The impact in Scotland would be bad enough. In Northern Ireland, it would potentially be even more dangerous. Boris Johnson styling himself “minister for the Union” might not be enough to stop a drift towards a united Ireland. Under the Good Friday Agreement, the Northern Ireland secretary must call a border poll if there is likely to be public support for the province to leave the UK. Karen Bradley, the previous holder of the post, warned May’s cabinet that a no-deal exit would make such a poll far more likely.

So Johnson is playing with fire. His own party might not care. Remarkably, a YouGov survey found that six out of 10 Tory members would rather Brexit happened even if it meant Scotland or Northern Ireland leaving the UK. So much for the Conservative and Unionist Party. It’s the Brexit Party now.

In 2015, the Lab-SNP spectre helped David Cameron win an unexpected overall majority, the high point of a career cut short by his unnecessary EU referendum. After winning the 2014 vote on Scottish independence, Cameron wanted to be remembered as the PM who kept Scotland in the UK and Britain in Europe. Will his legacy now be as the man who spectacularly did the opposite on both?

The only people who can prevent it are MPs. The union is yet another reason why they must find a way to prevent no deal when they return from their summer break next month.