UNIONISTS have stepped up calls for a boycott of the fledgling Citizens Assembly of Scotland just a day after its chair pleaded for sceptics to "give it a chance”.

The anti-independence Scotland in Union campaign became the latest voice recommending non-participation in the new forum in case it was “misused” by SNP ministers.

In a letter to its 26,000 registered supporters, the group said that unless the SNP could prove it was prepared “to act in good faith”, people should refuse to take part.

Chief executive Pamela Nash said that, given the SNP’s record, “We cannot see why the Scottish public should have any faith in this process or, indeed, take part.”

Last week, the Scottish Tories and Scottish Liberal Democrats both refused to have anything to do with the Assembly, calling it a “Nationalist Stunt” designed to promote independence.

On Monday, the Assembly’s first co-convener, former Labour MEP David Martin, responded by insisting the exercise would be “entirely independent” from the Scottish Government.

He said: “I have taken this on because I believe it is a genuine attempt to find out if there is consensus on some of the controversial issues facing Scotland….

“Give it a chance, let's see how it operates. I think it could make a big contribution to greater public understanding of the issues we face and perhaps build more of a consensus."

READ MORE: New chair pleads with critics not to boycott Citizens Assembly

However, opposition parties remain deeply sceptical of the Assembly, whose 100 members are supposed to start examining long-term challenges facing Scotland in the autumn.

Based on the Irish models which led to referendums on same-sex marriage and legalising abortion, the Assembly was announced by Nicola Sturgeon in April at the same time she published a new Bill paving the way for a second independence referendum.

Last month, SNP MP Joanna Cherry QC publicly described the Assembly it as “part of the process of preparing voters in Scotland for a second independence referendum”.

Ms Cherry today underlined her position by calling the Assembly the "perfect way" to get out of the Brexit impasse and move towards independence.

And when Constitutional Relations Secretary Michael Russell set out more details in Holyrood last week, he refused to say if the SNP Government would abandon independence if the Assembly requested it.

“I commit myself to listening to the assembly, being public about what it says, and ensuring that whatever it says is reported,” Mr Russell replied.

READ MORE: Tom Gordon: Citizens Assembly backlash is of the SNP’s making

Ms Nash, a former Labour MP, said: “Citizens Assemblies are growing in popularity throughout the world, and we have remained open-minded about the value of this approach in Scotland; any space where the views of the public can be examined and taken into account is to be welcomed.

“However, given the statements from senior SNP politicians, and the SNP’s consistent record of going against previous public consultations, many have expressed concern that the Citizens’ Assembly could be misused.

“If, before the assembly has been established, the SNP Government is already giving a strong signal that it will not accept the recommendations unless they happen to be in line with its own goal of breaking up the UK, then we cannot see why the Scottish public should have any faith in this process or, indeed, take part.

“If asked, unless evidence emerges that the SNP is prepared to act in good faith, we urge our supporters not to participate in the Citizens’ Assembly.”

The Assembly’s 100 members (and 20 substitutes) are intended to broadly represent the Scottish population and are supposed to meet over six weekends by spring 2020.

READ MORE: Scottish Tories urge boycott of Citizens Assembly, dismissing it as 'Nationalist stunt'

In Ireland, the work of the Assemblies led to several referendums.

However, Scottish Government officials last week admitted SNP ministers had not discussed any issue other than independence that might be put to a referendum in Scotland.

The Assembly is backed by the Scottish Greens, while Labour has given it a guarded welcome, seeking assurances it is not focused on Indyref2.

Green MSP Patrick Harvie said:  “Scotland in Union are an increasingly bitter and cynical outfit, who appear to have no interest in putting forward positive ideas for Scotland’s future.

“There must be many voters who support the union but who wish their political representatives would come up with something constructive.

"They should certainly have nothing to fear from doing so – the Citizens Assembly will expose all the options to scrutiny by people who’re not stuck in the party political bubble, and that’s the whole point.

“The proposal is that Scotland’s Citizens assembly will be politically independent, but can draw on advice from a diverse, cross-party team.

"If the main pro-UK parties take the same position as Scotland in Union, perhaps it just means that unionism has literally nothing left to offer.”

A Scottish Government spokesperson said: "The Assembly will be convened independently, will take expert advice, and we are committed to responding to its recommendations in a reasonable timescale.

"This approach is clearly set out in the principles that will guide all aspects of the work of the Assembly announced on 26 June.

“Citizens’ Assemblies are becoming an established way for mature democracies to engage with complex and contested issues on an inclusive, informed and respectful basis. That is what we want for Scotland.”