NICOLA Sturgeon is under pressure to back a referendum on Brexit after one of her closest political allies called on the SNP to support a second vote on the deal to leave the European Union.

READ MORE: Paul Hutcheon: backing a Brexit referendum could get the SNP off the constitutional hook

Noel Dolan, who was the First Minister’s enforcer in Government for nearly a decade, questioned why no SNP politicians were in favour of a policy backed by the Liberal Democrats as well as Labour and Tory figures. He wrote: “We should be campaigning for a second Brexit referendum.”

His comments were endorsed by Kevin Pringle, who was former First Minister Alex Salmond’s spin doctor, while party depute leadership contender Keith Brown said he had a “degree of sympathy” for the move.

Dolan’s call came as tens of thousands of Yes supporters marched in support of independence yesterday. The rally was one of the biggest in Glasgow since the Iraq war in 2003, with police estimating 35,000 in attendance. Reports from campaigners, however, claimed up to 90,000 attended.

Paul Hutcheon analysis: Why backing a Brexit referendum could help the SNP

The rally highlights a potential gulf over future direction and strategy. The grassroots are eager for the SNP to set a date for a second independence referendum soon, but many party insiders and senior officials want to wait until the post-Brexit picture becomes more clear. The rally also saw unionist campaigners stage a counter-demonstration. There were some ugly scenes, including a small group of men jeering at Yes supporters and giving a Nazi salute.

Sturgeon is considering her next constitutional move amid growing confusion over the details of the Brexit deal to be struck between the UK Government and the EU.

READ MORE: Paul Hutcheon: backing a Brexit referendum could get the SNP off the constitutional hook

She backed another independence referendum immediately after the Brexit vote in 2016, but she rowed back from her preferred timetable after a disappointing general election result.

The First Minister could back an early referendum on Scotland leaving the UK, or further delay the plan. She is expected to announce her intentions in the autumn.

However, senior figures in her own party believe the priority should be halting Brexit, rather than giving the electorate another vote on independence in the short-term.

Dolan joined Sturgeon’s team in 2004 when she was depute SNP leader. After the SNP secured power in 2007, he became Sturgeon’s policy adviser in Government and became her senior special adviser, both as Deputy First Minister and when she succeeded Salmond as First Minister in 2014.

READ MORE: Paul Hutcheon: backing a Brexit referendum could get the SNP off the constitutional hook

Dolan, dubbed “his master’s voice” in a reference to how close he is to Sturgeon, was her most trusted adviser and was known to fight her corner in Government. He retired in 2016. He wrote: “Labour, Tory, Lib Dem and Green MPs are campaigning for a second referendum on leaving the EU. Why are there no SNP MP/ MSPs getting behind this initiative?”

The SNP has argued that the UK Government’s EU Withdrawal Bill amounts to a “power grab” by Westminster, but Dolan wrote: “Without Brexit there is no ‘power grab’. We should focus on the main event – Brexit and not on the consequences. We should be campaigning for a second Brexit referendum. After all 62 per cent of the Scottish electorate voted to remain in the EU.”

READ MORE: Paul Hutcheon: backing a Brexit referendum could get the SNP off the constitutional hook

The Dolan approach would require Sturgeon to shelve plans for a second independence referendum until Brexit is resolved. Pringle, who along with Dolan was a highly influential figure in the Salmond administration, is also in favour of a second referendum.

Sturgeon has not backed another vote on the EU, but she has dropped hints her party could embrace the policy. She said last year: “I don’t think we’re there yet but this is something that will be discussed and debated.”

She went further in a radio interview in January: “I’ve also said previously and I’ll say it again today that I do think that as the situation develops the argument for giving people a say on the final outcome may become irresistible”.

READ MORE: Paul Hutcheon: backing a Brexit referendum could get the SNP off the constitutional hook

MP Ian Blackford, the SNP group leader at Westminster, has also made positive noises about another referendum.

He said recently: “We are open to looking at it but I don’t want to get deflected from the challenge of staying in the single market and customs union, because that’s where I believe we can build the consensus.”

Willie Rennie, the Scottish Liberal Democrat leader, told the Sunday Herald: “Noel Dolan is right that we should be trying to stop Brexit rather than just trying to cope with the consequences. The SNP should put independence to one side and get behind the growing numbers of people who want a referendum on the Brexit deal.

READ MORE: Paul Hutcheon: backing a Brexit referendum could get the SNP off the constitutional hook

“I hope Nicola Sturgeon is listening to her former close advisor. Perhaps it’s a clue as to what she really thinks, perhaps Noel Dolan is still his master’s voice. The SNP have dodged the question for too long – will they back the Brexit deal referendum to stop Brexit.”

Labour MP Ian Murray, a leading supporter of the People’s Vote campaign which wants the electorate to have its say on the final Brexit deal, said: “This is a hugely significant intervention from one of Nicola Sturgeon’s closest confidantes. There are Labour, LibDem, Green and Tory MPs campaigning for a People’s Vote on the Brexit deal, and it’s time the SNP put its own narrow party interests to one side and did what is best for the people of Scotland and the UK.”

An SNP spokesperson said: “Scotland voted overwhelmingly to remain in Europe – with remain majorities in every single part of the country – and that result has to be respected. The Tories must not be allowed to use it as an excuse to restrict or remove the powers of the Scottish Parliament. All parties serious about defending devolution should unite in that cause. The SNP will continue to fight to keep Scotland in the Single Market, backing jobs, living standards and our economy - and keeping the pressure on the Tories who have no mandate here.”