Former Labour MEP, David Martin, has branded the Conservative and Liberal Democrat parties "foolish" for their boycott of Scotland's new Citizens's Assembly.
Mr Martin, who is co-convener of the new Assembly, said that while it would make "no difference" to its function, the parties should not "turn their heads away" from the new body.
His remarks came as it was announced recruitment of Assembly participants had begun. with a "cold-calling" process which will see researchers randomly knock on people's doors to ask if they want to join.
Between 100 and 120 members of the public - excluding elected politicians, staff or officers of political parties and civil servants - will be recruited from across Scotland and from different ethnic, social and economic backgrounds, to be broadly representative of the Scottish public. Thousands of people are expected to be asked to get involved before the quota of members is reached.
They will be tasked with finding answers to questions such as how Scotland can "overcome the challenges we face, including those arising from Brexit?" and "what kind of country are we seeking to build?"
However the Assembly has already faced opposition from the Scottish Tories who have described it as a "talking shop for independence" while Willie Rennie, leader of the Scottish Liberal Democrats has labelled it "an attempt to sew some new patches on the SNP's dodgy case for independence."
It has also been embroiled in controversy after SNP MP Joanna Cherry declared it the "perfect way" to move Scotland towards independence, and pollster Mark Diffley - who runs a polling company with former SNP Westminster leader Angus Robertson - was revealed as the person who won the £22,000 contract to select the Assembly members.
Mr Martin - who lost his European Parliament seat earlier this year - said the lack of participation by the two parties "makes no difference because this is not a forum for political parties, it makes no difference to the function of the Assembly" but he stressed "they would be foolish to turn their heads away.
"Almost one in five of participants - if we're successful in recruitment - will be historic Conservative voters and I'm not sure how they would feel about their party to say we're having nothing to do with this."
His co-convener Kate Wimpress added: "That perception is out there but I would point to the recruitment framework - that undercuts that assumption. People will be giving of their time, engaging in this debate, it would be foolhardy to ignore that."
She added: "I sincerely hope people will see this as a positive chance to look at some of the important issues that are facing us all, in a supported space, where we can look at the complexities of the world and step away from the binary is it this or that? It's an opportunity. I genuinely hope people will see it as that."
However Adam Tomkins, Scottish Conservative constitution spokesman, doubled down on his party's opposition to the Assembly, and said it will "never be viewed as impartial".
He said: “As we’ve just seen with the GERS figures, the SNP will contort anything to try and support their separatist agenda. The SNP believes the constitution is the most important priority but the majority of Scots simply want the Scottish Government to tackle our worsening education system, worst ever hospital waiting lists, crumbling roads and faulty children’s hospital.
“If this Assembly is considering options to improve Scotland’s future why aren’t they considering health, education or climate change? The simple fact is that the SNP’s destruction of our economy and public services are the biggest threats to the successful future of Scotland.”
The Assembly conveners also stressed that the topics for debate would be led by the members, and that there would be no discussion on an independence referendum.
Mr Martin said: "The government has made a decision to ask for a Section 30 order, that's not for us to debate. It's not for us to come to a conclusion on independence, or devo max, or even going back to a unitary state. The Assembly will look at topics, for instance it might want to look at immigration and the impact of Brexit on that, and take evidence and come to a conclusion."
The selection of participants will see 15 per cent of members drawn from the Lothians, 14 per cent from north east Scotland, 13 per cent from Glasgow, a further 13 per cent from the west of Scotland and an equal percentage from the south of Scotland, 12 per cent form Mid Scotland and Fife and Central Scotland and eight per cent from the Highlands and Islands.
In terms of age the largest cohort at 26 per cent will be from the 45 to 59 years-old bracket, and there will be more women than men, with percentages of 52 per cent to 48 per cent.
Around 96 per cent of members will be of white ethnicity, there will be quota targets for those with disabilities and mental health issues, and in terms of qualifications, the vast majority - 52 per cent - will be educated to secondary school Standard and Higher grades, with just 31 per cent having degrees, and 16 per cent expected to have no qualifications.
Politically the Assembly will be "broadly balanced", using the average percentages from opinion polls over the last 12 months, so 30 per cent will be SNP voters, 18 per cent Conservative voters, 16 per cent Labour, six per cent Liberal Democrat and four per cent Green voters. Undecideds and even those who wouldn't vote in a Scottish Parliament election will be represented.
And in terms of voting intentions in any Scottish independence referendum, the Assembly will consist of 45 per cent of No voters, and 40 per cent Yes, with the rest being made up of don't knows and those would not vote.
There has been no estimated cost of running the Assembly yet given - and yesterday it was revealed that no criminal checks will be carried out on participants as the organisers have no legal remit to do so.
Each participant will be expected to attend six weekend residential meetings, which start in October, receiving £200 for each session plus expenses, and help with childcare or caring duties - which could see the bill for participants top £120,000. Already the bill for consultants has reportedly hit £250,000.
Ian Davidson, a civil servant seconded to act as the Assembly's secretariat, said they were not authorised to use the official disclosure checks on criminal records.
He added: "There are certain limitations on the extent to which we can investigate members of the Assembly. They will be required to sign up to a code of conduct. They will be required to confirm that there is nothing about their profile that would bring the Assembly into disrepute.
"We will not be investigating their background but we will have safeguarding in place, but if people are debarred from participating in this for whatever reason the responsibility is on them to come forward and identify restrictions - and also if restrictions subsequently come to light we will act upon them.
"It's incredibly important to think about, not just aspects of criminal records and background checks, but even people's participation in Twitter and so on, because there will be a degree of scrutiny, so as well as previous conduct we will ask them to think about their participation on social media during the Assembly and encourage them strongly not to comment on their participation."
Mr Davidson stressed that "people aren't debarred from participation in these kind of activities because of a past criminal activities", however he said if there were legal restrictions that prevent people participating they would expect them to be declared. He added: "People's safety will be protected [at the residential weekends] because we will run these proceedings professionally."
Ms Wimpress, added: "The whole point is they're randomly selected. There will be checks and balances, but we want to have a mini public we want to have a set of people who represent the country as it is.
And Mr Martin said: "At the end of the day we want a picture that looks like Scotland, like it or not some people in Scotland have criminal records, that will make it a genuine cross-section of society."The Scottish Greens have welcomed the remit for the new Citizens’ Assembly, but urged the Scottish Government to back proposals for the same approach in response to the climate emergency.
Scottish Green co-leader Patrick Harvie welcomed the commitment for the Assembly to be inclusive, transparent and be able to set its own agenda.
“It is essential that the Citizens’ Assembly is empowered to be able to discuss what it wants and set the agenda on issues outwith the party-political bubble, so I’m pleased it will be able to have its own voice," he said. "I also welcome the commitments on it being transparent and independent from government."