For the Better Together campaign, time is everything.

As support ebbs away, Unionist calculations turn on the pace at which opinion is shifting and on the number of days remaining until September 18. For No, ground is being lost. The question is: how much and how quickly?

As politics, this isn't exactly inspiring, but those who would defend the United Kingdom are in no position to be picky. They can't claim to have won hearts or minds over the past year. They can't say that they have made a case, positive or negative, that has converted more people than it has alienated.

Loading article content

Their only boast is that they are still ahead. Now they have two months left in which to hang on to a diminishing majority.

It won't make for a pretty spectacle. Most of the big scares have been tried, but there will be a couple in reserve. Risible effusions of undying affection are suddenly all the rage (sometimes "better late than never" is a poor excuse) but we haven't heard the last of them, more's the pity.

Obnoxious attempts to portray anyone liable to vote Yes as an ethnic separatist simmer away, meanwhile, heedless of the damage being caused to the body politic, and in sharp contradiction to the claim that we are and must always be "better together". What is the line, exactly? Please don't go, you appalling proto-fascists?

Never mind. Once you understand the caveats required for reading opinion polls, you see a contest that has "tightened", albeit in fits and starts, as the months have passed. The differences between the findings reported by various companies have been big enough, often enough, to merit debate on September 19, but the tale of converging numbers has been common to all. The tale has a moral to it. If Scottish Labour is sitting uncomfortably, we'll begin.

The latest TNS survey suggests that 28 per cent of those who supported the party in the elections of 2011 have decided to vote Yes in September. Labour lost those elections, you'll remember, and lost them badly. Seven seats were forfeited as a big chunk of the party's vote migrated to the SNP. Now TNS says that still more voters - up from 21 per cent on previous polls - are choosing to reject Labour's advice and its campaign for the Union.

You could ask several questions. Have these voters considered Ed Miliband's offer of "the best of both worlds" and decided that the best doesn't amount to much? Have they concluded that David Cameron's chances of forming another government in 2015 are improving by the week and chosen to repudiate the Union as a consequence? Is the very idea of "Labour Scotland" now just a myth, and a flimsy one? Or are these voters simply inspired by the idea of self-determination?

You could almost take your pick. Depending on the circles in which you move, you can hear variations of these themes in many parts of Scotland.

The 2011 elections were certainly a clue that the "Labour vote", the old web of allegiances and beliefs, had become a shadow of its former self. This helped to turn the SNP into a majority government. But it did not mean, still does not mean, that a mass conversion had taken place.

After all, the 28 per cent identified by TNS represents people who stuck with Labour in 2011. They were part of the minority who were not convinced by Alex Salmond, his party, or, come to that, the promise of a referendum on independence.

These voters supported Labour in the Holyrood elections knowing full well that the bulk of the party and its leadership had set their faces against self-determination. Now those voters switch. Whether the referendum is won for the Union or lost, the future for Scottish Labour looks tricky.

It is not without problems for Yes Scotland. That campaign will need to bear the prior rejection of the SNP in mind. To win still more of those who voted Labour previously - for such is now the essence of the game - it will need to go on asserting that the independence movement is more than Mr Salmond, that many non-nationalists intend to vote Yes, that the proposition is a bigger deal than any political party.

Plenty of Yes supporters already make that case. It is one big reason why Better Together talks endlessly of Mr Salmond and of nothing else. Charmingly, that Unionist campaign insists on describing anyone voting for independence but disinclined to support the SNP as a mere dupe. The TNS survey says the tactic is looking threadbare.

For those who once stuck by what used to be called traditional Labour it has been a long road. As often as not, their votes have been taken for granted. In government - as now in opposition - the party has sought to fashion an appeal to an electorate far beyond Scotland.

Miserable wars and banking crashes have tested loyalties to the breaking point. The idea of solidarity, the key argument against independence, has had plenty of lip service, but Labour's leadership has had other priorities. That has not gone unnoticed.

Besides, the SNP's Nicola Sturgeon has made the point explicitly. Anyone who wants a Scottish Labour Party responsive to Scottish voters needs to give serious consideration to independence. We've had "the best of both worlds" for generations. We've seen what has become of Labour in Scotland. A pick and mix of "more powers", like a bag of stale sweets, doesn't begin to answer the problem.

The fundamental numbers produced by TNS can be interpreted, up to a point, according to taste. No has 41 per cent, Yes has 32 per cent. That's a hefty difference. But a gap of nine points was 19 points only last September. Before the psephologists set to work to work "stripping out" those who remain unsure, meanwhile, the poll finds that 27 per cent, a decisive group, remain undecided. Given the movement among former Labour voters, straws in the wind are hard to ignore.

Every poll is just one poll. Aggregations of the various surveys do not explain the differences between them, least of all in this contest. What can be observed is that TNS has not often led the pack in detecting momentum for the Yes campaign.

Now it finds that Labour's message - Labour's message specifically - is failing to convince some of those who trusted the party as recently as 2011, when the SNP was slipping below most radars and fashioning a majority.

Lurid insults towards former upholders of "the Labour vote" won't do Better Together much good at this stage of the game. The scares and the ill-disguised threats of a bitter tomorrow if we achieve independence are wearing off like cheap hooch.

A hangover for Scottish Labour will ensue. It will not be cured by any number of fatuous "love bombs". When a party likes to address itself to the people, it runs the risk that the people will begin to take themselves seriously. Just one poll. There will be plenty of others before we are done. But Scottish Labour had better prepare itself for news from the heartland.