More than a dozen official briefing papers have been drawn up by the Scottish Government to prepare for a second independence referendum, it has emerged.
But ministers are refusing to publish the documents, prompting opposition claims of a lack of "transparency and open government."
Officials insist that they need "private space" to allow a full and rigorous debate within government about all the issues, before ministers reach a policy decision.
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But they acknowledge that 13 documents have been drawn up in response to a Freedom of Information (FOI) request seeking details about work on a second referendum.
Simon Elder of the Scottish Government's Constitution and UK Relations Division states in his FOI response to the Conservatives that there is a "public interest in the topic of a second independence referendum."
He adds: "I am satisfied that after taking account of all of the circumstances of the case, there is a greater public interest in ensuring high quality policy and decision-making by Government, and this is achieved through allowing Ministers and officials the private space they need to consider all available options and to debate those rigorously and to fully understand their possible implications, before a final position can be reached."
But he also states: "I can confirm that 13 other documents were identified as being within scope of your request."
Nicola Sturgeon has stated that she had ordered civil servants to begin work on a second referendum in the aftermath of the Brexit vote two years ago and is adamant that Scots will have a second vote on leaving the UK when the terms of Brexit are clear. But the constitution remains the responsibility of Westminster and Theresa May has stated she will not allow a second vote on Scots leaving the UK.
Scottish Conservative chief whip Maurice Golden said: “These secret briefings prove that the prospect of a second independence referendum is never off the SNP’s table.
“The question was settled in 2014. Yet, in the years afterwards, civil servants were still churning out briefings for ministers so they could continue banging the drum for separation in front of the cameras.
“That is irresponsible government. “Instead, the nationalists should have been putting all their efforts into improving schools, hospitals, infrastructure and the economy.
“The SNP government clearly deemed it necessary for taxpayer-funded civil servants to produce these highly-political briefings.
“As such, they should now be published, as part of the SNP’s so-called commitment to open and transparent government.”
The Tories have now submitted an appeal to the Information Commissioner.