For many of its advocates devolution was supposed to strengthen the Union. By showing that the United Kingdom could accommodate the distinctive needs and wishes of Scotland, it was hoped that Scots would be persuaded they could pursue their aspirations and secure political recognition of their distinctive national identity within the framework of the Union. Yet on May 3, 2007, just eight years after the creation of the devolved Scottish Parliament, the Scottish National Party, the principal advocate of Scottish independence, topped the poll and its leader, Alex Salmond, was elected the country's First Minister. It would seem that the most crucial foundation of the Union of all - public support - is now close to collapse.

Does the SNP "victory" last May indicate that the introduction of devolution has served to undermine public support for the Union in Scotland? Over the past decade typically only around three in 10 Scots have said they would prefer Scotland to be independent. The most popular option has consistently been some form of devolution within the framework of the United Kingdom. Moreover, there is not any sign of a trend over time, gradual or otherwise, towards greater support for independence. While there was some indication in 2005 that this might be happening, with support reaching 35%, the independence tide has subsequently ebbed again (our evidence comes primarily from the Scottish Social Attitudes Survey with access to the provisional data from the 2007 survey conducted after the May election).

On the basis of the figures, it seems that a more powerful parliament within the framework of the Union would most likely emerge the winner in any future "multi-option" referendum in which people in Scotland are invited to choose between independence, a more powerful version of devolution and the status quo. It seems there is considerable support for changing the way in which the devolved institutions are financed. In recent years, more than half have consistently agreed with the proposition that "now that Scotland has its own parliament, it should pay for its services out of taxes paid in Scotland". Only one-quarter appear to be opposed. This is despite the fact that government statistics suggest (albeit not uncontroversially) that current levels of public expenditure in Scotland outstrip current tax revenues.

While a clear majority of Scots may want to remain in the Union, and while there is some evidence that they may have become more persuaded of the economic and financial benefits of membership, this does not mean that there is not pressure for change. The Scottish Parliament is widely regarded as weaker than it should be, and as a result there is considerable public support for increasing the powers of the institution, including its financial powers. Evidently, a key challenge now facing the Union is whether it can accommodate this public mood.

The SNP may be committed to making Scotland independent, but its election to office does not seem to have signified growing public discontent with the Union. If anything, in some respects at least, the Union now appears to be regarded in a somewhat more favourable light than it was eight years ago.

This finding is not, in fact, as paradoxical as it might seem. First, it should be remembered that, while the SNP came first in the 2007 election, it still won less than one-third of the vote. Its tally was just 32.9% in the constituency contests and 31% on the list vote. The party was simply the largest minority in that election, rather than anything approaching a majority.

Secondly, while the SNP's share of the vote in the 2007 election might have been some nine to 10 points above the tally the Nationalists achieved in 2003, support for other parties that favoured independence, most notably the Greens and the far left, fell back substantially. Taken together, the increase in support for parties favouring independence was a far more modest three points on both ballots.

Indeed, while fewer people may have backed independence in 2007, those who did were far more likely to vote for the SNP than they were four years previously. In 2003 only just more than half (51%) of those who said they favoured independence voted for the SNP on the regional list vote. In 2007 no less than three-quarters (76%) did so. This change more than compensated for the impact of the apparent decline in support for independence. At the same time, however, the SNP also won an important slice of additional votes among the much larger group of people who supported devolution.

Nearly one-quarter of those who favoured some form of devolution voted for the SNP, up by nine points on 2003.

Given the mood among many who support devolution, the ability of the SNP to secure the support of those who do not support independence should not surprise us. For many, devolution was not providing as powerful a symbol of Scotland's distinctive national identity as they would like to see. However, it appears to have been among this group that the SNP did relatively well; those in favour of devolution but also backing more powers were twice as likely to vote for the SNP (28% did so on the list vote) as those not in favour of more powers (14%).

The SNP has always outpointed other parties in Scotland when people are asked how closely the various parties look after the interests of people in Scotland. For example, in 2007, nearly one-quarter (24%) said the SNP looked after those interests "very closely", while well under one in 10 said the same of any other party. It has thus, perhaps, always had the potential to appeal to those who, while still supportive of the Union, would like the apparent balance of power between Westminster and Holyrood reversed. Meanwhile, now that it has taken office, the SNP minority government has proved willing to state its disagreements with a policy stance being taken by the UK Government in public, in stark contrast to the rather coy approach taken by the previous Labour-Liberal Democrat coalition.

But if in so doing the SNP can persuade people in Scotland that the devolved institutions can be made more effective and that Scotland's voice in the Union is now being heard more loudly, perhaps they might be encouraged to believe that devolution within the Union can deliver - so long, perhaps, as the institutions are invested with a little more autonomy. By causing more friction within the Union, the SNP could ironically help persuade the public that remaining within that Union continues to be worth while.