AFTER three hundred years of union, Scots are to be given the chance to vote for independence. The offer of a legally-binding referendum, probably in 2014, comes from David Cameron, who is not just prime minister of the United Kingdom but also leader of an outfit formally known as the Conservative and Unionist Party. It is more than a remarkable concession. Since the Scots may indeed plump for independence (see article), it is also quite a risk. Mr Cameron's move has not, however, been met with overwhelming gratitude in Scotland. Widely described as a "Westminster Eton toff" north of the border, he is suspected of setting a trap by trying to bounce Scotland into a vote on terms that would tip the balance in the union's favour. Mr Cameron wants a straight in-or-out question. Alex Salmond, Scotland's first minister and leader of the Scottish National Party (SNP), which dominates the legislature in Edinburgh, is not so sure. He has said he favours a simple question. But he also points out there is a powerful view in Scotland that the country ought to be given more powers, taking it just to the brink of independence - "devolution max," as it is known. Perhaps the referendum should reflect this view by offering three choices. Or perhaps two questions should be asked at the same time: whether Scotland should become independent, and whether it should acquire more powers. It is easy to see why the nationalists are keen to muddy the clear Scottish waters. Polls suggest that Scots are keener on more power than on outright independence. Give them three options, and the unionist vote could split, possibly producing a plurality for independence. Whatever the result of the vote, Scotland would surely end up with more powers. The SNP would have delivered something to its nationalist supporters. But anything other than a straight in-or-out question may result in a damaging wrangle. What if, in a three-part question, independence wins - but with only 35% of the vote? What if 51% of Scots vote for independence, but, in a second question, 80% vote for more powers? Nationalists would interpret that as a mandate for independence. But Westminster could fairly argue that Scots apparently prefer further devolution to outright independence. Scotch, neat, no ice A simple question also makes for straightforward campaigning. The Conservative, Labour and Liberal Democrat parties would have to explain why union is good for Scotland - something they have so far done poorly, which is one reason they are in headlong retreat north of the border. The SNP, for its part, would have to explain the problem to which independence is the solution - which they haven't done either. And if the Scots turn down independence, they can later be asked if they want more devolution. Mr Cameron's question, then, is the right one. And he should have a say on the referendum's terms. Divorces affect both partners. Scottish independence would have mighty consequences for Britain, raising questions from how to settle the two nations" fiscal accounts to where the Royal Navy's nuclear submarines should be parked, if not in Scotland's deep lochs. Canada has a sensible model for moving towards independence: its government has passed a law which sets various conditions on any future referendum on Quebec's independence, including that the question should be a clear one. If most Scots wish to leave Britain, so be it. But it must be a clean divorce, not a long, finger-pointing row that hurts everyone.