Under pressure on Europe and sterling, the first minister has switched focus again on independence: claiming a written constitution answers the 'why' question on leaving the UK

Alex Salmond has suggested that independence could see Scotland's citizens given substantial new constitutional and legal rights, embedded in a new written constitution. It is a proposal which excites lawyers, and again opens a further front in the referendum battle.

In another carefully-chosen set piece speech in London, again to the Foreign Press Association, Salmond tentatively unveiled further details on Wednesday about what that constitution might involve: policies designed to appeal, it seems, chiefly to left-of-centre voters and policies too reflecting his own political priorities.

Were he to lead Scotland's first independent parliament in 2016, the first minister would want to enshrine a right to free education and to a home, guarantee a future Scottish government could not send troops to fight illegal wars (like Iraq), and (as previously billed) make it illegal for Scotland to hold or use nuclear weapons.

He told his audience:

...we will make Scotland's constitution an early signal of how the people of Scotland will use the powers of independence – to take our place as a good global citizen, to protect and affirm the values we hold dear, and to create a fairer and more prosperous nation. That is a key part of the 'why' for independence for Scotland.

He claimed that Scotland was different from its English neighbour:

For centuries, Scotland has had a distinct constitutional tradition - first expressed in the Declaration of Arbroath in 1320, reaffirmed by the 1989 Claim of Right for Scotland, and most recently restated by the Scottish Parliament just one year ago. That tradition states that the people of Scotland are sovereign and that they have the power to determine the form of government best suited to their needs. It stands in contrast to the UK principle that parliament has unlimited sovereignty.

It would be "one of the first duties of the parliament of an independent Scotland to establish a convention to draw up that written constitution," he said.

Only a post-independence constitutional convention would be able to draw in all Scotland's different civic, political and social institutions into the debate; in typically expansive mood, his proposals were just one contribution to that:

The reason for this is that Scotland's constitution should enshrine the people's sovereignty and affirm the values and rights of the people, of the community of the realm of Scotland. Since no single party or individual has a monopoly on good ideas; all parties, and all individuals, will be encouraged to contribute.

For John Drummond, who has championed a written constitution for Scotland as chair of the Constitution Commission pressure group, and has blogged on this for the Guardian, focusing on the detailed policies Salmond misses the truly radical proposition: the move to place sovereignty with the people and not (as the UK's constitution has it) in the parliament.

It's absolutely fascinating: it's a game changer. He's taken the debate away from identity and nationalism, and is [now] taking about better governance. And the appeal of better governance I suspect will find resonance amongst the third [of voters] who are not committed, so it's a game changer.

Drummond was previously irritated by Salmond's reluctance to force the debate forwards now, not later.

After all, setting up a new constitutional convention after May 2016, itself over three years away, which will then take perhaps a year or more to decide on that constitution and provoke intense disputes between power blocs in Scottish society, will delay this well into the life of a new Scottish state.

Drummond says he now sees the logic in waiting until the referendum. He suspects the Scottish government and, by implication, the pro-independence campaign, will work up further detail on that constitution before referendum day. His group will certainly "bang the drum" before then.

He can do nothing other from a legal point of view. He could start some work but only the parliament can form a convention because if you're looking to have a process which is as fundamental as this, when sovereignty is being transferred from a political entity to the Scottish people, then there needs to be a great deal of involvement by the parliament.

Patrick Harvie, the Scottish Green party co-convenor and an SNP partner in the Yes Scotland pro-independence campaign, sees it differently:

The timescale for developing this is crucial. At the moment the suggestion seems to be that this is something we could work on once sovereign powers have been transferred following a Yes vote, but this would imply a dangerous period of constitutional vacuum. The first minister is right to say that the process of writing a constitution should engage all of Scotland, and not just political parties, but for that to happen we should aim to inspire people now with a picture of how other countries such as Iceland have gone about this in a radically democratic way.

Some of Salmond's other political opponents reacted with derision. Alan Cochrane, the Daily Telegraph Scotland editor, insists Salmond is being deliberately vague and wholly disingenous. These guarantees would bind future generations to ever expanding costs.

Guaranteeing free education by law would cost Scotland £150m in extra university tuition fees for English, Irish and Welsh students under EU rules, his paper reports. There is already a legal obligation on councils to house the homeless; what would a constitution add?

It is designed to create a wholly bogus atmosphere that suggests that independence is actually a probability and not the extreme long shot that the current opinion polls predict. In addition, Mr Salmond's aim [was] to portray himself as some great democratic reformer, rather than just another politician on the make.

Willie Rennie, the Scottish Liberal Democrat leader, picks up a similar theme: in promising all these new state-funded privileges, Salmond has failed to make his sums add up and explain how they will be funded.

The promise of a constitution on free education and housing means nothing given that figures researched by the Scottish Liberal Democrats over the New Year showed thousands of young Scots turned away from colleges and hundreds of families living in B&Bs because of the cuts imposed by the SNP government. Alex Salmond has full powers to sort this out right now. At this rate Alex Salmond appears to be on course to be the first defendant to be prosecuted in his own constitutional court.

Many judges and senior lawyers think Salmond exhibited quite ill-judged aggression and antipathy towards the judiciary and human rights lawyers in his tirade against the UK supreme court, criminal solicitors and in particular the campaigning human rights lawyer Tony Kelly in 2011.

His government is under fire now for its handling of some key civil rights: access to legal aid is being cut (heavily and unjustifiably say defence lawyers); plans to abolish corroboration in criminal trials is under attack from police and lawyers alike; other lawyers remain very uncomfortable with Salmond's electorally popular decision to abolish double jeopardy – allowing people to be retried for crimes for which they had previously been acquitted.

Salmond is again seeking to out-flank Labour and the Lib Dems: accentuating, he hopes, the proposition that Labour and the Lib Dems are intellectually conservative, even illiberal on civic rights.

Yet the rights Salmond floated on Wednesday are already SNP policies and some actual law now: his opponents insist he's chosen to pick the shiniest of low-hanging fruit and ignored his own government's troubled record on other civil rights. So while there is great enthusiasm in legal and constitutional quarters for this proposal, there are some tougher questions on live policies Salmond may find even more difficult to avoid.