The former deputy leader of the SNP Jim Sillars has said the UK Government will never allow another Yes/No referendum in Scotland.

Speaking to The Herald, Mr Sillars said strategic considerations would mean the UK Government insisting that a form of devo-max was on the ballot paper next time.

“The last time the UK Government thought it was a skoosh,” said Mr Sillars. “Next time, they know this is much more serious and I don’t think our people have realised just exactly what’s at stake for England and the importance of Scottish independence to English security – it’s about the bases, the ability to use Scotland as an unsinkable aircraft carrier.

“Then there’s the seat on the security council of the UN. These are two major strategic issues south of the Border and we’re not going to have a simple independence against the status quo – we’ll have a much more sophisticated counter argument.”

Speaking to The Herald about his new memoir, Mr Sillars, a former Labour MP who won Govan for the SNP in a by-election in 1988, also said the SNP wasn’t being realistic about the timing of the next referendum. “We’ve had nothing but talk of a referendum since the morning after the Brexit vote in 2016 and it’s never happened,” he said. “And now this deal Nicola has with the Greens makes it ‘impossible’ for Boris Johnson to say no. I don’t understand where she gets her ideas from. The arithmetic is the same whether the Greens are in or out. I’m not sure Boris Johnson even knows who Patrick Harvie is.”

The other problem, according to Mr Sillars, who voted Alba at the last election, is that the clock is ticking on the SNP’s record in government.

“The ability of the leadership to spin out the constitution in front of everything else is now limited. And I think they’re likely to unravel over the next 12 to 18 months because of the incompetence. There’s a point where a community will not accept the incompetence under which we’ve been governed. Some people said to me they held their nose and went into vote SNP this time. And that’s the first sign.”

Asked where the SNP’s problems started, Mr Sillars, who voted Alba at the election, pointed to the parliamentary inquiry into the Scottish Government’s investigation into harassment claims against Alex Salmond. “I think it began to unravel then,” he said.

“Not the whole population, but significant sections, journalists and the legal profession, began to realise the Crown Prosecution Service was not what we thought it was. We also saw significant abuse of governmental power – the refusal to hand over papers, the conduct of Humza Yousaf as justice secretary actually tweeting abuse against Jackie Baillie during a quasi-legal process.

“The hubris is there. The SNP on education has not done well, we’ve regressed. On health, they’re engaged in a world of pretence – the health service has got real problems. Housing, we haven’t solved the problem. We’ve declared war on poverty so many times and have been defeated so many times but don’t admit it. The PR is there. The incompetence is there. They’re engaged in managerialism but the fact is they’re not very good at it.”

Mr Sillars, who was married to the SNP MP and MSP Margot MacDonald, has also talked in his memoirs, called A Difference of Opinion, about his concerns that the First Minister has focused too much on emphasising grudges and grievances rather than trying to work more co-operatively with the UK Government. He said the SNP also needs a much more detailed plan for independence if it is to have any chance of winning a referendum.

“Where is the thinking going on?” he said. “Where is the debate? The discussion? I don’t think Alex Salmond’s government really thought about what the Scottish economy would be in terms of difference post-independence and I don’t think we’ve had a very good look at it. The argument is at the yah-boo level: ‘you’ll be skint’, ‘no we won’t’. We’ve never said: let’s have a look at what we’ve got. Would we operate on the same basis post-independence? Would our priorities be the same as they are now?

“I think that the cult of personality over the years, particularly in Nicola Sturgeon’s period, has emptied the intellectual capability of the SNP. It’s hollowed out intellectually and lives on a diet of PR, virtue and gestures. Look at when NS said the troops should stay in Afghanistan – it’s just for a headline.

“Five minutes thinking seriously about it, it’s absurd. All that mattered was the headline. Nicola had something to say. Does anybody in the party have the ability to say: what the hell you saying that for? I don’t think anybody can say it.”

In The Herald Magazine on Saturday: The life and turbulent times of Jim Sillars