Is there any bribe or blandishment that the Tories will not use as the prospect of losing a quarter of their kingdom looms? In last week's budget, a sinister new low was reached by the Tories, brutish and un-British in its conception. It was an obvious response to recent polling on the independence referendum, which has consistently shown that working-class people are more likely to vote yes. It's the "let's just jolly well ensure that the blighters stay out of the polling booths on 18 September by enticing them into pubs and bingo halls" strategy.

There are occasions when the rest of us get to see what Britain looks like through the eyes of David Cameron and George Osborne. When they occur, they are delightful to behold and should be cherished. Thus last week we learned that, to David and George, Britain's less affluent neighbourhoods look like a painting by Hogarth. There they all are: the women spilling out of gin palaces, their children starving in their arms, their menfolk spending what remains of their benefits on a last slurp of ale and a squeeze from a dancing girl. It can only be a matter of time before tax relief can be obtained from keeping whippets and pigeons.

No prizes for guessing what will be the theme for the fancy dress party at the next Tory party conference: braces and bingo. The ladies will be encouraged to wear red crimplene twinsets and large cards with the numbers 66 and 11 prominent. Their swains will arrive in white vests and ill-fitting suit trousers held up by braces. Some will have gone to the trouble of drawing a pencil-thin moustache under their noses; others will have a cigarette taped behind their ear. And so, just a few days after Michael Gove expressed astonishment at the Etonian influence in Cameron's circle, Osborne's entertaining mini-budget for the oiks proved his point beautifully.

The Tories unveiled their vision of life beyond SW1 just as it was being revealed that, six months before the referendum, the gap between the yes and no vote, according to a poll by Panelbase, has narrowed to only 5%.

The momentum shift in the campaign, which has been evident since the start of the year, has now built a head of steam for the nationalists. At last year's SNP conference, a former senior party adviser told me: "If we are to attain our goal next September, then the numbers really ought to be changing in our favour round about March and April."

That the SNP now have the wind at their back as they turn towards the home straight is no real surprise following a lacklustre campaign by Better Together, lacking either imagination or enthusiasm. This, too, was easily predicted. How do you galvanise Labour activists into showing enthusiasm for the red, white and blue and a union dominated by a party whose road map out of recession rests on hammering the poor and mollycoddling the rich?

Their consistent portrayal of poor and backward Scotland being swamped by the tides of economic uncertainty first merely attracted ridicule before beginning to become irritating. Now it appears to have alienated many of the previously uncommitted.

Perhaps this is why Jim Murphy and Gordon Brown were brought in last week. Little has been seen or heard of Murphy previously during this campaign and absolutely nothing of Brown. So lamentable was the performance of each, though, that it seems probable we will not hear much from either again. Bizarrely, Brown, the man whose light-touch regulation of the UK banking sector encouraged the greed, corruption and larceny that now characterise them, portrayed the SNP as a rich man's party. Then he claimed that lower- and middle-income Scots families would be "£1bn pounds" worse off in the event of independence. Brown, as a former UK chancellor, knows more than anyone, though, that Scotland has raised more tax per head than the UK as a whole for the last 33 years.

Murphy, meanwhile, who has never had a job outside Labour machine politics in his life, came away with this one. "I've become increasingly scunnered," he said, "as I listen to the SNP talk about the communities I grew up in and telling them that everybody will be better off when in truth the opposite is the case". "Scunnered" is one of those words that the chattering classes use only when they want to get down and dirty with the people. It is frowned upon at the type of schools to which Labour ministers usually send their children. Murphy, of course, will also be prominent among those Scots Labour MPs who will lose their Westminster jobs, salaries, cars, expenses and researchers, in the event of a yes vote and who will have to seek a nice, safe constituency in Northumberland or some such.

Now it falls to the Labour leader, Ed Miliband, to make the case for the union. His speech on Friday seemed to signal the end of the tone of negativity that has characterised the Better Together campaign thus far, which has got them nowhere and which has put them into reverse. His intervention may be too late, though. The two areas in this campaign where the yes campaign enjoys a huge advantage are in funding and number of activists. If the yes vote can encroach to within five points of no without the nationalists having yet to deploy fully their two most potent weapons then the future for the union looks bleak indeed.

Miliband must hope that enough Scots have sufficient faith in his ability to deliver a Labour Westminster majority next May to pledge continuing loyalty to the union. A Labour majority would be required to guarantee added powers for Scotland; a minority would leave them beholden to the little Englanders in their party defending slim majorities.

The nationalists also have another ace to play and one that may be displayed on billboards in the last few weeks of the campaign in the same manner of the Tories' "Labour Isn't Working" slogan from 1979.

On this, a large picture of Cameron would appear and alongside him his own words from last year: "It would be wrong to suggest that Scotland could not be another successful, independent country." It's that kind of positive campaigning to which Miliband must aspire.