HOW does a campaign avoid sounding negative, while persuading Scots to vote no in the referendum on independence?

That is the central challenge for the Better Together campaign, launched jointly yesterday by the Labour, Liberal Democrat and Conservative parties.

Alistair Darling, recalled from his political back seat to front this pro-UK campaign, is a good choice for the job, not only because of his undoubted commitment to both Scotland and the UK but also because he is a well-respected political heavyweight, capable of taking on Alex Salmond . There is steel beneath that calm and apparently mild-mannered exterior. As a former chancellor, he is well-qualified to make the UK case on the economy, the area where this campaign is likely to be won or lost.

Yesterday's launch provided a solid start, avoiding the razzmatazz of the Yes Scotland event. Instead of a star-studded line-up, its focus was on the "quiet majority".

Mr Darling had a fine line to tread, both accentuating the positive reasons for staying within the United Kingdom, while implying the potential risk and uncertainty of going it alone. His emphasis was on what unites us – "the ties that bind us": not merely friends and family, but institutions such as the NHS, the BBC , the Bank of England (founded by Scots) and the Army.

And like the child who gives the address "Scotland, UK, Europe, The World", he argues that being passionately Scottish and passionately British are not mutually exclusive. Indeed, his case is that we can be citizens on all these levels. He also asserts that Scotland's membership of the UK provides clout on the world stage at every level from Britain's impressive foreign aid budget to a seat on the UN Security Council. An independent Scotland could not match that clout.

The vocabulary of this speech was telling. Despite all the positive sound bites – "An idea worth celebrating", "a proud nation within a larger state", "best of both worlds" – it was, as the First Minister observed later, also peppered with negativity about the prospect of an independent Scotland: "uncertainty, separation, instability, upheaval".

Which of the competing visions will prove the more persuasive? As Mr Darling recognised, if his side of the argument is to carry the day, he needs to win it emotionally as well as intellectually.

Though the Better Together campaign may start as the favourite to win, it has work to do and pitfalls to avoid. It may have the advantage of being able to draw on the collective reach of the three pro-UK parties but it will struggle to paper over the divisions between them over the central question of what happens if Scots say no to independence. That is why a second question on the ballot paper remains a vital issue.

Ultimately, events beyond Scotland could decide this country's future. On the one hand, the ongoing eurozone crisis and global instability may persuade Scots that this is no time to be going it alone. (Little wonder that Ireland and Iceland have disappeared from SNP rhetoric.) On the other hand, Mr Darling faces the task of talking up the UK, just as David Cameron works up a vision of the nation under a future Tory government in which under-25s and those with large families will be left destitute if they cannot find work. In the end it will come down to one simple question: What is best for Scotland's future? It promises to be an intriguing contest, the result of which will determine our children's future.