Ever since the Scottish National Party's remarkable victory last May, Westminster has been in a state of shock, unsure how to proceed. But now, finally, David Cameron, determined not be remembered as the man who lost the Union, has resolved on a course of action . He will allow the SNP to stage its own binding referendum on independence on the condition that it is held in the next 18 months (any referendum after this date will be advisory, as it would always would have been) and that it offers a straight yes/no question on Scottish secession.
Cameron's move upsets Salmond's plans in several respects. The First Minister has long intended to hold a referendum in the second half of the Scottish parliament, perhaps in 2014 on the 700th anniversary of the Battle of Bannockburn, when he believes that discontent with the Tory-led government will be at its height. In addition, he planned for the ballot paper to feature two questions, one on independence and one on full fiscal autonomy or "devolution max". Aware that there may not be a majority for the former, the SNP leader is eyeing the consolation prize of "devo max", a stepping stone to full independence. But Cameron is determined to deny Salmond these two advantages. To add authority to his stance, he will publish a consultation paper later this week revealing legal advice that the referendum will only be binding if both parliaments agree to its timing and wording.
There is, of course, a risk that all this could backfire. Cameron's intervention could be seen as an attempt by the Tories - not a popular breed in Scotland - to hijack a referendum that the SNP has an electoral mandate to hold. It was an argument made at length by Nicola Sturgeon, Salmond's deputy, on the Today programme  this morning. But, as she conceded, there is a potential contradiction in the SNP's stance. It maintains both that Cameron has no right to dictate the terms of the referendum and that his move will backfire. But if Cameron's move will backfire why is the Scottish government so opposed to it? The answer, as Sturgeon will not say, is that the SNP is not convinced there will be a majority for independence in the next 18 months (or ever) and, consequently, is determined to reserve the option of devolution max. Yes, some Scottish voters will resent Cameron's intervention but others will ask, "why doesn't Salmond want an early referendum? What's the big feartie afraid of?"
Set against this must be the disorganisation of the pro-Union side (who will lead the No campaign? ) but Cameron has called Salmond's bluff and the initiative, for the first time in months, is with him.