In launching the Yes Scotland campaign in favour of independence yesterday, more than two years before the promised referendum, the First Minister, Alex Salmond, and his Scottish National Party set out to seize the initiative. The star-studded launch, supported by the Scottish Green Party and a host of celebrities, comes months before the No campaign is likely to get off the ground.

There will be opponents of independence who console themselves with the thought that the Yes campaign risks peaking too soon. That might be too relaxed a view. Mr Salmond has been consistently underestimated by his opponents, especially those in England. He is not only an accomplished political speaker, but also one of the shrewdest operators in the business. If anyone can win over doubters among his fellow countrymen, it is he.

Whether the Scots choose independence must, in the last analysis, be up to them – though the rest of the UK is entitled to express a view. But they should not decide to strike out on their own without having to hear the best case for preserving the three-century-old Union. The No campaign starts with two advantages here. A poll commissioned by Alistair Darling, the former Labour Chancellor, showed that only one-third of Scots, if they voted today, would support independence. There also tends to be a bias in referendums in favour of the status quo.

But there can be no room for complacency. The No campaign needs to organise itself, and fast. The Yes campaign before last year's UK referendum on changing the electoral system from first-past-the-post to the alternative vote offers a textbook example of how not to do it. It was late, lacklustre, poorly argued and inadequately publicised. It almost gave the impression that even the supporters' hearts were not in it. If a majority of Scots are serious about preserving the Union, they must get out there and make themselves heard.

There is no lack of professional Scottish politicians who could take to the stump for the cause. Indeed, one of the more light-hearted reasons given by English voters for supporting Scottish independence is the number of Scots who have served in successive UK governments. Mr Darling is one such. But we could also name Gordon Brown and Douglas Alexander from Labour; the former Edinburgh and now London MP Sir Malcolm Rifkind from the Conservatives, and Charles Kennedy, Sir Menzies Campbell and the current Chief Secretary to the Treasury, Danny Alexander, from the Liberal Democrats. All would have a tale to tell about the benefits of the Union.

And that tale needs to be told. The arguments of the Yes campaign have to be taken on directly, with the political implications and especially the economic implications of independence spelt out. There is no room for scare-mongering; small countries are viable, too. But exaggerated claims for the value of North Sea oil could be parried by some home truths about the hubris, once upon a time, of the Royal Bank of Scotland.

Above all, there must be clarity. The possibility that the referendum might include a third option, so-called devolution max – fiscal independence without an actual break – is to be resisted, as are hints from David Cameron that Scotland might be offered a pre-emptive form of devo max before the referendum. If Scots vote for independence, so be it. But there are reasons why the Union has endured for 300 years, and the referendum campaign presents a new opportunity to explain why it should survive even longer.