John Curtice: A solution that dare not speak its name

It is a curious battle. One side wants to keep alive an option in which it does not believe. The other side is insistent it be killed off, even though many of them would like something like it to happen.

Welcome to the paradox at the heart of the fierce dispute between the Scottish and UK governments about how the Scottish independence referendum should be conducted.

The cause of the controversy is "devolution max" – the idea that Scotland should become responsible for nearly all her own domestic affairs, but still be part of the UK, with defence and foreign affairs remaining the responsibility of Westminster.

Such a step would represent a huge change to the current devolution settlement, with important ramifications for the rest of the UK. But it would keep the Union together – and the UK's nuclear weapons in the Clyde.

It is not the Scottish National Party's goal. Mr Salmond, its leader and Scotland's First Minister, wants his country to be a player on the international stage – and nuclear weapons out of the Clyde. Nevertheless, he says that if someone can come up with a properly developed proposal for "devolution max", he is minded to put it before Scotland's voters.

There is a simple reason for his stance. The idea seems to be popular, far more so than independence.

According to the Scottish Social Attitudes survey, at least three-fifths of Scots believe the Scottish Parliament should take charge of taxes and welfare benefits north of the border, the two key areas of domestic policy still in Westminster's hands. Where the Scottish people draw the line is at the idea that Edinburgh should be responsible for defence and foreign affairs.

Equally, Ipsos Mori recently found that as many as 68 per cent back an extension of the Scottish Parliament's powers, whereas only 38 per cent support independence.

Winning a Yes vote for independence looks like an uphill struggle. In contrast, devolution max looks a sure-fire winner. Most supporters of independence are willing to back it, while at least half of those who want to stay in the Union prefer it to the status quo.

So although devolution max is less than Mr Salmond wants, it is much closer to his ideal than the current devolution settlement. If it were to be introduced, he could at least claim to have brought Scotland within sight of the promised land.

Therein lies the rub for his opponents. Instead of simply ensuring the SNP's dreams of "separation" are dashed for a generation, the independence referendum would give the nationalists a significant consolation prize – and leave them still able to fight another day.

But in insisting on a simple Yes/No vote on independence, unionists are playing a game of high-stakes poker. The outcome would turn on who could succeed in appealing to the one-third or so of Scots whose preference is to stay in the Union but who reckon their country should be able to run more of its domestic affairs.

The unionists' presumption is that these voters would stick with the Union. But, denied the chance to vote for what they want, they might begin to wonder whether a vote for independence is not the better option of the two actually before them.

Ironically, many in the unionist camp favour a significant extension of devolution. The Scottish Liberal Democrats have established a commission under Sir Menzies Campbell to look at "home rule". Labour's foreign affairs spokesman, Douglas Alexander, has given thoughtful speeches pointing his party in much the same direction, while the new Scottish Labour leader, Johann Lamont, has indicated she is open to the possibility of further devolution.

Yet, to a man and a woman, they all argue that more devolution should be pursued only when independence has been defeated. The trouble is, if unionists are not prepared to put the idea to the test now, will Scots trust them to deliver it later?

John Curtice is professor of politics at Strathclyde University