SNP members who believed Nicola Sturgeon could deliver an independence referendum in 2020 were “willingly misled”, the party’s former deputy has said.

Jim Sillars said credulous activists “should have known that if you go to the top of the hill for an impossible purpose, you have to come back down with nothing”.

He described the First Minister’s belated admission that Indyref2 might be some time away as a “capitulation to reality”, adding: “When a sinner repents, rejoice, don’t mock.”

After repeatedly talking up the prospect of Indyref2 later this year, Ms Sturgeon admitted on Friday that it may not happen, and urged her supporters to be patient.

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Boris Johnson has refused to grant Holyrood the power it needs to hold a new vote, saying the No result of 2014 was a once-in-a-generation decision.

Ms Sturgeon said she would still try to bring a new vote about this year, but also ruled out Holyrood trying to hold its own vote without Westminster’s consent.

She said she wanted a referendum that was “legal, legitimate and agreed”, whether it was in 2020 or at a later date.

Her climbdown led to a backlash from some senior independence supporters, including the Wings over Scotland website, which called her “The Betrayer” and urged her to quit.

In a letter to the Daily Telegraph, Mr Sillars said: “Stripped of its fluff, Nicola Sturgeon's speech was a capitulation to reality - no indyref2 until there is an overwhelming demand for it, wait until Brexit is done and digested, no illegality, and a longish road road ahead.

“She has been accused by those who marched up and down Scotland to her orders, as a 'betrayer.' The truth is they were willingly misled, and should have known that if you go to the top of the hill for an impossible purpose, you have to come back down with nothing.”

Mr Sillars, who backed Leave in 2016, said the SNP at Westminster now had to overhaul its tactics and find a way to get the best for Scotland out of Brexit, not merely condemn it.

He said the party’s MPs should avoid propaganda, study the EU-UK trade talks objectively, and form alliances with English MPs with similar interests.

He said: “They must abandon acting as a shadow fifth-column for Brussels as has been their role since June 2016.

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“To be effective, the SNP group has to be listened to by the UK government.

“That will require a change in tone and tactics, moving from grudge and grievance, accepting Brexit has happened, stop insulting the chief Leaver, the PM, as a liar, and seeking positive outcomes.”

He suggested these could include “free trade zones in Scotland as well as NE England, making sure changes in state aid and procurement policies benefit local business, and jobs, in gaining from public contracts.

“To the latter we can add fisheries, where, on both, it will be wise to create alliances with English MPs, whose areas have the same interest as the Scots.”

Rather than independence, he said the immediate issue for SNP MPs was deciding whether to “back or oppose and try to weaken the strong pre-negotiation stand taken by Boris Johnson”.

He added: “This is a new opportunity for the SNP Westminster group to become relevant. I hope they take it.”

A former Labour MP who won a famous byelection for the SNP in Govan in 1988, Mr Sillars served as Alex Salmond’s deputy leader in the early 1990s.

An SNP spokesperson said: “The people of Scotland voted overwhelmingly for an SNP manifesto committed to an independence referendum this year – that is the democratic mandate which should be respected and which Boris Johnson is running scared of.

“We are being dragged out of the world's biggest single market against our will – becoming an equal, independent member of the EU will protect and build a more prosperous society. It's imperative that Scotland now has the right to choose that better future."