Willie Rennie accused her of failing to ‘explore all options’ as promised in the wake of the vote.
The First Minister has “broken” the cross-party Holyrood consensus built in the wake of Brexit, the Scottish Liberal Democrats have claimed.
Party leader Willie Rennie said he gave his backing to Nicola Sturgeon to negotiate directly with Brussels on the premise she would “explore all options”.
He has now accused her of only being interested in independence.
On June 28, Sturgeon held a special vote in the Scottish Parliament asking for a “mandate” to deal directly with the EU, which was supported by the Lib Dems, Labour and the Greens.
Writing in the Scotsman newspaper, Rennie said he and his party colleagues had backed the motion in good faith having been “reassured by the First Minister that the motion was ’emphatically not’ about independence”.
Since the vote, he said Sturgeon has “talked about little else, betraying those words she uttered in parliament and consigning the consensus to the dustbin”.
He said if he was to be presented with the same motion again he would tell his party to vote it down.
Rennie also said the Lib Dems would block legislation for a second independence referendum.
The First Minister hit back and claimed Rennie was siding with “Tory Brexiteers”.
She insisted her position remains unchanged andthe Lib Dem leader’s criticisms of the expert group were “deeply misplaced”.
Rennie wrote: “Nicola Sturgeon has broken the Scottish cross-party consensus that was built after the Brexit result just two months ago.
“When my Scottish Parliament colleagues and I cast our votes at the end of a special parliamentary sitting in favour of exploring the options, we were reassured by the First Minister that the motion was ’emphatically not’ about independence.
“But, from that moment on, she has talked about little else, betraying those words she uttered in parliament and consigning the consensus to the dustbin.
He said “even the Martians know” the First Minister wants independence but said he thought he may have been able to find common ground with her on an alternative solution
Rennie also questioned the First Minister’s motives for setting up an expert group to explore post-Brexit options for Scotland, saying he had not seen a single recommendation from the group.
He said: “The First Minister appointed an expert group with some credible figures with a wealth of European experience, so the early signs were positive that she meant what she said.
“I have received no invitation from the expert group to seek my opinions. I have not even heard a single recommendation from that group.
“They risk becoming little more than a book cover for another independence campaign manual.”
He added: “The First Minister only wants their reputations, rather than their advice, to take another step towards independence.
“If the First Minister was serious about exploring all options she would have set them out and discussed them in public.
“She would have asked for my opinion on my preferred option. She would have asked her expert group to engage.
“I would have expected to hear more about Norway, Greenland, Switzerland or a special UK solution.”
The Lib Dem leader concluded: “If there was another vote in parliament on the same motion we would vote No.
“And when she brings forward her legislation for another independence referendum we will vote No to that, too.”
Rennie’s comments were “profoundly mistaken”, the First Minister insisted.
A spokesperson for Sturgeon said: “It is perhaps not too surprising that the Lib Dems are siding with Tory Brexiteers over the interests of Scotland – as students south of the border know to their cost, Liberal Democrat promises of support are not worth the paper they are written on.
“However, the fact is that Willie Rennie is profoundly mistaken – and his criticisms of the independent expert group, which met earlier this week, are deeply misplaced.
“The position the First Minister laid out on June 24, and which Mr Rennie backed in a parliamentary vote, is unchanged.
“The First Minister is clear that protecting Scotland’s interests and our place in Europe is her starting point.”
The spokesperson added: “Indeed, she has appointed a dedicated minister to lead this process.
“However, she has also been clear that the option of independence should be on the table if it becomes clear that it is the best or only way of safeguarding our interests.
“Clearly, Willie Rennie thinks we should stick with Westminster regardless of the damage it does to our interests.
“Mr Rennie also says he wants us to consider his preferred solution – we would be happy to do so and invite him now to state, in detail, exactly what it is and how it would work.
“Until today, his silence has been deafening.”
The Scottish Conservatives said it was “clear from the outset” the First Minister would use Brexit to promote independence.
The party’s deputy leader Jackson Carlaw said: “It’s been clear from the outset that the SNP were using the EU referendum result to support their independence agenda so I’m surprised it’s taken Willie Rennie this long to realise.
“Nicola Sturgeon is attempting to twist the disappointment felt by many Scots over the EU result into support for separation but Scots did not vote to Remain to allow the SNP to take Scotland backwards into another independence referendum.”
The Scottish Greens suggested Rennie was “flouncing away in a huff”.
The party’s external affairs spokesperson Ross Greer MSP said: “The lack of any significant change in the Brexit situation appears to have prompted the leader of Holyrood’s smallest party to flounce off in a huff.
“This is hardly the responsible attitude Scotland needs at this time. Thankfully, the Scottish Greens remain at the forefront of the campaign to keep Scotland in Europe. Over 30,000 people signed our petition calling on Holyrood to explore every option.
“I look forward to the statement from the First Minister next week on the European situation and the entire Green MSP team will continue to engage constructively with the Scottish Government and other interested parties.
“All avenues must be exhausted to maintain Scotland’s international links, and our social, economic and environmental protections.”
Greer added: “If the Lib Dems would rather side with a hapless UK Tory Government, they’re welcome to that.”