Who would have thought that a referendum on independence would be this tricky?

We have Calman going through Westminster, Devo Max still floated by nobody but somehow not disappearing and now Devo Plus, the same but different, being pushed to the fore today by former Lib Dem MSP Jeremy Purves.

Ardent supporters will no doubt largely scoff at this proposal while ardent unionists will largely support it if it means full independence will fail. I just hope that somewhere between the two that a real consideration of what is being proposed takes place as the original document from Reform Scotland that Devo Plus is based upon is an excellent piece of work and is that rare thing – a unionist solution that is sensible, lasting and sustainable.

Devo Plus, if I am not mistaken, will give Scotland control of all of its income tax and corporation tax and fund its own spending accordingly, including control of borrowing powers. So there would be no problems with raising one tax rate but not raising another, no complaints about a one size fits all UK policy on Corporation tax and there would be no limit to spending tomorrow’s money today if the Government of the day decided this was necessary, perish the thought.

It’s such a shame therefore that this option follows the Cameron-esque strategy of being a potential solution ‘if Scotland votes no in a referendum’, a carrot for Scots to aim for while we are beaten with the stick into the No vote. Aside from not having as full a debate as we could do come 2014, this is a mistake tactically for anyone in favour of the United Kingdom remaining in place.

The more options there are before Scots in the referendum then the less likely it is that independence will be the final decision. All things being equal, there is a 50% chance that Scots will vote Yes to independence but if you were to include the clearly defined Devo Plus on the ballot slip, that chance reduces to 33.3*%. Today is a better day for David Cameron than it will be for Alex Salmond.

Devo Plus won’t kill nationalism stone dead. It won’t provide a seat at the EU or the UN or give Scotland a fairer share of MEPs for example and it won’t remove nuclear weapons from north of the border, and there will always be a sizeable element of Scots campaigning for those things and more besides.

But for this once-in-a-generation referendum and for those Nationalists who will be satisfied with nothing short of full independence, this Devo Plus has the potential to be a game changer.