NICOLA Sturgeon has harmed the SNP by putting “short-term PR gains” ahead of its long-term strategic goals, according to the party’s former deputy leader.

Jim Sillars said the First Minister should stop “grandstanding” over Brexit and a second referendum and work consensually to secure more powers for Holyrood instead.

Writing in the Herald, Mr Sillars also said the UK would be “daft” to give the SNP government a seat in Brexit talks, as it had shown itself to be a “potential cuckoo in the nest”.

The stinging attack comes as Ms Sturgeon prepares to set out her next steps for a second referendum in light of the SNP’s worst general election reversal in almost 40 years.

The party lost 21 of the 56 seats it won in 2015 and its vote share fell from 50 to 37 per cent, as the Unionist parties gained seats in a backlash against her referendum plan.

The First Minister is expected to push back a referendum until well after Brexit talks conclude in late 2018 or early 2019, but leave open the possibility of a new vote by the 2021 Scottish election, when her mandate to hold one expires.

She is due to speak at a conference in London today titled “Brexit - the road ahead”.

However she promised in March that she would tell MSPs her plans first, suggesting a statement to Holyrood tomorrow or Thursday.

Mr Sillars, who was SNP deputy under Alex Salmond in the early 1990s, said it had been “painful” to watch the party “self-inflict an electoral wound” by demanding a referendum most Scots didn’t want.

He said threatening Brexit legislation by withholding a legislative consent motion (LCM) at Holyrood would also be “a serious mistake” and “further self-harm”.

Ms Sturgeon has demanded her government have a seat on the UK’s Brexit negotiating team, with a view to keeping the UK, or at least Scotland, in the EU single market.

But Mr Sillars, who backed Leave, said that was a lost cause, as Ms Sturgeon had sided so strongly with Brussels after the Brexit vote.

He wrote: “Making Scotland Brussels’ insider friend may have pleased many of my fellow party members, but meant that when hard confidential negotiations get underway, the UK Government would be daft to invite a potential Brussels cuckoo in the next.

“A short term tactic which played well in Brussels, fell flat in London, which is where Scotland really needs leverage.

“Sadly, short term PR gains leading to longer term strategic losses have been a marked feature of the Sturgeon leadership. Indyref2 was the classic example.”

He also said Ms Sturgeon erred by joining the Supreme Court action over Brexit last year, when the court ruled Holyrood could not veto Brexit by withholding an LCM.

He said if the First Minister had kept out of it, there would still be a useful uncertainty over whether a veto was possible.

“Instead, another line in the sand was washed away, leaving future threats looking increasingly empty and hollow.

“The time for grandstanding is over. Scotland’s interests will be best served by building a wide consensus of national support for powers presently held in Brussels to come to Edinburgh, powers that can help our economy to grow.”

Former Scottish cabinet secretaries Kenneth MacAskill and Alex Neil have also advised Ms Sturgeon to park a second referendum because of its unpopularity with voters.

However in a newspaper column yesterday, Ms Sturgeon stuck by her rationale for a second referendum, saying Brexit, in whatever form, would be deeply damaging to Scotland.

She wrote: “Whatever deal is reached, Brexit will be enormously damaging when it comes to jobs, investment and all our living standards. And I fear that will become clearer now with every week that passes.”