IT'S not a premise those of a Nationalist disposition would in any way accept but, it seems, it is an issue beginning to seize the minds of more and more Unionist politicians.

That is, what happens should Scots reject independence? Do people say, that's it, game over; Britain's constitution is settled for another generation? Or could it just be the start of a new process?

Remarkably perhaps, there appears to be a growing consensus – SNP aside for obvious reasons – that a rejection of Scottish independence will create the opportunity to have a long, hard look at the UK's creaky, complex and anomalous constitution.

Earlier this month, Douglas Alexander, the Shadow Foreign Secretary, suggested the establishment of a Scottish convention to look at Scotland's future now all the pro-Union parties, with the Tories in the slow lane, are looking towards advocating greater powers for Holyrood.

However, his colleagues at Westminster want to go further and widen this out to a UK constitutional convention that would look at a raft of issues, not just whether there should be more powers to Holyrood, but also whether it is possible to address the so-called "English question" and devolve more powers to England, sort out the highly sensitive issue of the Barnett Formula and at long last deal with House of Lords reform.

The McKay Commission looking at the old constitutional chestnut, the West Lothian Question, appeared to come up with nothing in particular and ended up where we find ourselves already, ie, with a system full of anomalies.

Earlier this week, the Commons Political and Constitutional Reform Committee asked if there should be a convention to sort things out and said there was "some argument" for one, but made clear the English Question had to be addressed first.

Yet Professor Vernon Bogdanor, the constitutional experts' constitutional expert, noted that with an asymmetrical system, the English Question simply cannot be answered. He also called for a UK-wide constitutional convention, as the "future of Scotland should not be seen in isolation from that of the rest of the UK". It could even "strengthen the unity of the UK".

Sir Malcolm Bruce, who claims – wink, wink – to have had support for a convention from not only the back benches but also the front benches of the Lib-Con Coalition, wants a wide-ranging inquiry, but says it could be in different stages – Scotland first, England second and Lords reform later, perhaps.

Indeed, his LibDem colleague Alistair Carmichael, the Coalition's deputy chief whip, while also in favour of a UK-wide convention, does not want the potential of a tortoise Lords reform slowing down the hare of further powers for Holyrood. So we could get a staccato convention.

If Scots do indeed reject independence, then it looks certain all of Scotland's parties will, to varying degrees, be calling for greater powers for Holyrood; the Nationalists will adopt the next best thing and fall into federalist line.

Lord Forsyth, former Tory Scottish Secretary, suggested in the Lords this week that should there be a cavalry charge towards devo-max, then there would have to be – Lord help us – another referendum, but this time on a UK-wide scale.

Lord Wallace, the LibDem Advocate General, appeared to concede the point, suggesting those south of the Border would need a "buy-in". Of course, the SNP would point out the answer is simple: just say yes. If people do, a convention for the rUK might still be unavoidable as one would probably be needed to sort out what is left of the constitution south of the Border.