In the London Olympic velodrome last week, David Cameron expressed his love for the Union and called on English citizens to phone a friend in Scotland urging them to vote No to independence.

The Prime Minister is perfectly entitled to his point of view, wherever it is expressed. However, he should have the courage of his convictions and express them also in debate in Scotland with Scotland's First Minister.

Leaders' debates have become an established feature of modern mass democracy. The PM has declared that he is leading the Unionist campaign. By refusing to engage with Alex Salmond, Cameron is not only showing discourtesy to the Scottish people, he is damaging his own cause. It is to suggest that Scotland's national leader - elected by a landslide majority - is not worthy of the PM's time.

The failure to engage is not the worst aspect of the Prime Minister's Olympic speech. He said a lot about the past, but very little about the future constitutional settlement if Scots do indeed reject formal independence. Where are the "further powers" that he promised only this time last year? Scotland looks in vain for any sign from the Unionist parties that they are making a positive case for rejecting independence.

The Scottish Liberal Democrats have made some efforts to propose more powers, but they clearly have little influence on their Coalition partners in Westminster. Had it been otherwise, perhaps the Liberal Democrat Business Secretary, Vince Cable, might have usefully outlined them last week instead of making threats about the pound. Labour appear divided, with Scottish Labour MPs refusing to endorse the Scottish Labour Party's tentative proposals on devolving taxation.

Meanwhile, the No campaign has resorted to increasingly dire warnings about banks leaving, supermarket prices rising, pensions not being paid - even war in Northern Ireland.

And we have the Prime Minister raising fears about "customs checks" and "changing money" at the Border, when it is the UK Government that is making threats about the currency and refusing to discuss a stable transition, as called for by the National Institute of Economic and Social Research last week. This will not do.

This referendum is not, contrary to what the PM appears to believe, about identity or culture. Scots are quite comfortable with their dual identity as Scottish and British. We have no problems with Team GB. What the referendum is about is political power - the right of Scots to govern themselves, to the extent that such is possible in the modern world. It is the power to oppose welfare changes like the bedroom tax, immigration controls that damage Scottish universities; the power to promote Scottish economic wellbeing by controlling the levers of taxation; the right to reject weapons of mass destruction.

If David Cameron fails to understand this, he may well find that, when he next rings Scotland, the phone is off the hook.