Since then, two polls from the respected YouGov and a third this week from TNS all point towards the pro-independence Yes Scotland campaign narrowing this gap or even taking a slim lead.
How did it come to this? And with nine days and counting until the referendum what should each side do to get its message across and clinch victory?
The polling should not come as a shock. For more than two years the pro-union Better Together campaign has held a lead but that has gradually been reduced in the past nine months as the Yes campaign made steady if unspectacular progress.
There's an interesting strategic contrast in how the two campaigns have built support. Yes built a grassroots movement early by empowering volunteers. It gave them the materials and advice on what to do, but then left them to it and trusted them to get on unsupervised. That’s a big ask, especially for political strategists who can tend towards control-freakery.
Better Together took a more top-down approach, building a grassroots organisation that reports back to the centre, and relies on the existing infrastructure of the main UK parties.
The Yes campaign eschewed received wisdom on referenda that says the side proposing change needs a substantial lead in the final weeks of a campaign because experience shows some Yes voters will make a last minute switch to No.
Instead, Yes has consistently said it will build an irresistible momentum that will peak on 18 September rather than beforehand.
Recent polls bring an interesting twist. If No has indeed fallen behind this may be a timely reminder there is no room for complacency and every vote counts to save the union. Yes has always been the underdog but now may have to cope with becoming a favourite perhaps a fortnight too soon. The challenge becomes maintaining a lead instead of closing a deficit.
So with nine days to go it looks and feels in Scotland like it's game on – what should the two campaigns do?
Media commentators and backbench MPs are suddenly full of advice on radical action for the pro-union side, but is there really enough time to develop, implement and communicate a new strategy that is comprehended and accepted by undecided voters?
A change now is a big risk. We'll find out next week whether the No side can successfully explain Gordon Brown's proposal for more powers and whether voters will trust something that lands on the table so late in the day.
Better Together started campaigning on two levels: the risks and uncertainty of independence, and that Scots already enjoy the best of both worlds. They'll stick with that too.
Yes Scotland's worked in phases – Scotland could be independent, it should be independent, and Scotland must be independent. They believe phases one and two have been achieved and it's now about convincing voters of the third.
Now's the time for both sides to talk directly to as many people as possible and get their voters turning out – door-knocking, telephone calls and personal endorsements.
Social media, advertising and mainstream media all play supporting roles, but personal contact is the most powerful tool. That's why thousands of volunteers on both sides are speaking to hundreds of thousands of voters every week.
It's going to be closer than many expected, and whatever the result the communications strategies will give PR professionals two great case studies for years to come.
Alastair Ross is a director at Pinsent Masons and secretary for the Association for Scottish Public Affairs