Jeremy Corbyn is just as much to blame as Theresa May for the Scottish referendum

David Cameron hoped his legacy would be pulling the economy back from the brink, keeping Scotland in the UK and Britain in the EU. He achieved his first goal, although it could be in jeopardy if the economy falls off a cliff after the hard Brexit towards which we seem to be careering.

We know what happened to his EU goal, and his catastrophic decision to call a referendum on membership of the bloc now threatens to destroy his achievement in preserving the UK in the 2014 referendum on Scottish independence.

Another referendum in Scotland is inevitable in the next few years; it is only a matter of when. Theresa May cannot say no, which would merely boost support for independence and allow Nicola Sturgeon to call an advisory referendum. The two most powerful women in the UK are now two scorpions in a bottle; only one will get out alive. The one who loses the referendum will almost certainly have to resign, as the departure of Cameron last year and Alex Salmond in 2014 tells us.

The prospect of Scotland breaking away is real, and now taken very seriously in Downing Street. The opinion polls are close. The Yes to independence camp started the last referendum on 27 per cent. After Brexit and Donald Trump, we cannot assume lazily that “the Scots would not be stupid enough to leave”. Anything could happen. People took a chance on Brexit and Trump; they felt they had nothing to lose. They might do the same on independence. Project Fear warnings by the political establishment about the collapsed oil price, Scotland’s budget deficit, waiting for EU membership and pledging to join the euro might not cut much ice. Nor might predictions of a 10-year hit to the economy; the UK might suffer that anyway after Brexit.

Already the campaign feels very different to 2014. Sturgeon is a more appealing figure than Salmond. She is canny. Her decision to go for broke on Monday wrong-footed May. The No to independence campaign lacks an obvious leader and risks being dominated by Conservatives.

Brexit has changed everything. May has played into the SNP’s hands by allowing the drift to hard Brexit seem unstoppable. As a Remainer, she was overanxious to appease the Europhobes in her party. Give them an inch and they take a mile; some now press her to leave the EU without a deal, a reckless gamble. May’s decision to leave the single market – and not telling Sturgeon before she announced it – tipped the SNP scales in favour of another referendum. Sturgeon might seek single market rather than full EU membership in order to placate voters who want independence but not Europe.

So if Scotland votes to leave, May’s response to the Brexit vote will be one of the causes. Her eyes were on her own party, so she paid lip service to an agreed approach with the Scottish government.

History will also point the finger of blame at Cameron for holding an unnecessary EU referendum. But someone else is culpable: Labour. It has taken its Scottish heartlands for granted for too long, paving the way for the SNP to seize 56 of Scotland’s 59 seats at the 2015 general election. That is not Jeremy Corbyn’s fault but Labour’s failure to fight back since then is. He deepened Labour’s Scottish crisis at the weekend by saying that another referendum would be “absolutely fine” if the Scottish parliament voted for one (as it will next week). Corbyn unwittingly gave the impression that Labour backed a referendum, angering many of his MPs and cutting the legs from under Scottish Labour, which opposes the move. Then, as usual, he blamed his mistake on the media.

Corbyn’s decision to let through, without a real fight, the bill allowing May to start Brexit talks, also played into the SNP’s hands. True, he had a terrible dilemma, given that many Labour voters in northern England backed Leave. But with the Liberal Democrats decimated in Parliament, Labour’s feeble response so far has entrenched the SNP’s position in Scotland as the real opposition to hard Brexit. Corbyn is regularly outshone in the Commons by Angus Robertson, the SNP’s leader in Westminster, as he was again today at Prime Minister’s Questions, when Corbyn failed to exploit the Government’s handbrake turn on National Insurance contributions for the self-employed.

Something else has changed since the 2014 referendum. Then, there was a realistic prospect that Labour would soon form the next government. Today Labour looks a million miles away from power; the Conservatives could easily rule for 20 years. That could prove the SNP’s trump card. If the Scots break away, it could push Labour further into the wilderness as a new Westminster parliament minus Scottish MPs cements Tory hegemony.