HUMZA Yousaf today unveiled the latest paper in the series setting out his government's case for independence.

The 59-page document was devoted to the arguments why an independent Scotland should have a written constitution in line with the 27 members of the European Union (and unlike the UK) and the process that would take place in putting such an arrangement in place.

It said that developing a draft written constitution would be the task of a convention set up after independence with the final document going to voters for approval - or not - in a referendum.

In his speech in Glasgow outlining the proposal Mr Yousaf said a written constitution could include the protection of workers' rights to strike and a guarantee healthcare that is "free at the point of need".

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The First Minister also made clear the Scottish Government would want a new constitution for the country to rule out Scotland being a home for nuclear weapons.

Perhaps most eye-catching, in light of the new King's coronation last month, was the prospect that Scots could ditch the monarch as head of state and replace him - or any subsequent monarch - with an elected head of state as Ireland ultimately chose to do after exiting the UK.

For observers of Scottish politics there is much of interest in the document. However, there was something of a sense of unreality about today's press conference and the paper in light of an absence of a clear route to achieving independence given the UK Government's failure to agree to a new vote and the Supreme Court's ruling that Holyrood does not have the power to hold a vote on its own.

A task for the First Minister is to try and build support for independence without people knowing how that end point can be reached.

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The argument he made today, and indeed also during the SNP leadership election, is that by persuading more Scots to back the Yes case,  getting levels of support to a sustained majority - this itself will put pressure on a Conservative or new Labour government to agree to a second independence referendum.

With the Tories and Labour reluctant to agree to any new vote in the coming years, such a plan appears rather over optimistic on the First Minister's part.

But nevermind the challenge of building support for independence, with the police investigation into the SNP finances continuing to dominate the headlines, the party could yet face the prospect of declining support for its key ambition.

So far a number of polls have suggested that while the police investigation has been damaging to voters' support for the SNP it has not negatively impacted on support for independence. This is a situation that may change.

As once some Yes supporters begin to shift from the SNP to Labour, which pollsters suggest is beginning to happen, there is no guarantee they will continue to support independence.

It's entirely possible having switched support for parties this group of, probably soft Yes voters, may then decide to embrace Labour's plans for constitutional change, such as greater devolution. To them those proposals may seem both more realistic and achievable in the short term than the long road of independence.

Such an outcome in turn could prove highly damaging to the SNP's support.