Constitutional affairs spokesman Michael Russell today insisted that the Assembly would be independent from the Scottish Government as a key principle of its establishment as he revealed that former Labour MEP David Martin is to co-convene the proposed body.
The planned Assembly of 120 ordinary Scots will look at the way forward for Scotland as the Government sets out plans for a second referendum on independence. A similar initiative in Ireland was pivotal in bringing about the legalisation of abortion.
But the Tories and Liberal Democrats today ruled out taking part. Tory constitution spokesman Adam Tomkins said the proposal amounted to "yet another national conversation on Scotland's constitutional future."
He added: "We've heard it all before and here we go again.
"Last week we heard that one of the lessons from Ireland is that to be effective, Citizens Assembles need cross-party buy-in at he beginning of the process.
"Well this one does not have that - this is not a genuine attempt at a Citizens Assembly in Scotland.
"It is a Nationalist stunt to kick-start the conversation about independence.
"I'm afraid that we will have nothing to do with it and I urge all unionist parties in Scotland to see this for what it is - and give it a wide berth."
Lib Dem leader Willie Rennie also ruled out his party getting involved.
"We are not participating in this latest SNP exercise," he said.
"It has been set up simply to patch up the SNP's case for independence. Taxpayers money should not be used for this party political process."
Mr Russell said he regretted the decision of the pro-union parties not to get involved.
He announced that Mr Martin would be co-convener of the Assembly, with a female co-convener to be appointed.
He told MSPs the principles of independence from Government would be a key one for the Assembly, along with transparency, inclusion, access, balance, cumulative learning and open-mindedness.
"A growing number of people are seriously considering the issue of independence," he said.
"This government is determined that people of Scotland are supported to make choices about their future with full access to the facts they need."