Is Scotland seeing a Quebec effect?
Support for Scottish independence has surged by four points in the latest opinion poll.
The survey conducted by Survation for the Daily Mail put "Yes" on 42 percent, "No" on 48 percent, with 11 percent saying they are undecided. Once the "Don't Knows" are excluded "Yes" are on 47 percent, "No" on 53 percent.
As Strathclyde University's Professor John Curtice points out on his "What Scotland Thinks" blog, this equals Survation's all-time high vote for "Yes". Furthermore, it is the fourth successive poll to show strengthening support for independence.
With the referendum just three weeks away, the "Yes" campaign is now pulsing with energy.
Scotland's First Minister Alex Salmond hasn't stopped grinning since the second leaders' debate, shown live on television on Monday evening.
Even the usually hostile Daily Mail declared that he had "crushed" his opponent, former UK Finance Minister Alistair Darling.
The pro-UK Better Together campaign might have hoped to retake the news agenda on Wednesday with a letter from 130 business people arguing that the business case for independence "has not been made".
What happened next was a spectacular PR own goal.
Better Together produced an election broadcast about an indecisive mother who is overwhelmed by politics. It was intended to focus the minds of undecided voters, and particularly women, on the uncertainty created by independence.
Opponents - and even some supporters - saw it as condescending and sexist. Within hours, the hashtag #PatronisingBTLady was trending on Twitter as social media users posted some viciously funny responses.
Then, the Scottish Secretary Alistair Carmichael raised more eyebrows, announcing that he would resign from the government at Westminster in the event of a "Yes" vote and join Alex Salmond's Team Scotland to negotiate the terms of independence.
If there is a "Yes" vote on September 18, political observers will look back and see this as the week when the ground began to shift.
You might call it the 'Quebec effect' because a similar thing happened when the Canadian province held its own referendum on sovereignty in 1995. The conventional wisdom of most pollsters that support for the change option falters as polling day gets closer was turned upside down.
As in Scotland, early polls indicated a comfortable "No" victory. But the "Yes" campaign enjoyed a late surge, rising from 39 percent a month before the vote to 44.5 percent on the eve of the referendum.
One factor was the number of women who moved from being undecided to supporting "Yes."
Canada's federalists eventually carried the day but the final margin of victory was less than one percent.
In a close contest the "get out the vote" operation on polling day will become crucial. This will be a challenge for the nationalists because "Yes" support appears to be highest in working class districts with a traditionally low turnout.
They need as many people to vote in the poor east end of Glasgow as the affluent west end of Edinburgh.
One veteran left-wing activist, Eddie Truman, told me that: "'Yes' voters are the mostly highly motivated part of an electorate I've ever come across in more than 30 years political activity."
The next three weeks are likely to be very uncomfortable indeed for those who want to see the UK stay together.