The No campaign will win by a wider margin than the opinion polls predict. So says Ruth Davidson, the leader of the Scottish Conservatives: for in her view those who refuse to answer the pollsters’ questions – the undecideds and the don’t knows – are in reality closet Noes.

She spoke yesterday lunchtime in the relative calm of Coldstream, the town just inside Scotland on the north bank of the River Tweed where the famous regiment was raised by General Monck in 1650 as part of the New Model Army. Almost everyone round here intends to vote No, for to introduce passport controls at the bridge over the river would be an intolerably disruptive and destructive measure.

We shall know on Friday morning whether Davidson is right, but after two and a half years of campaigning she seems remarkably calm: calmer, one might say, than some of the Tories in London. In her view “people in Scotland are really fair”, so have waited for a long time for Alex Salmond to answer their questions about independence, before the realisation has dawned on them that he is not going to give any answers.

Davidson is a Member of the Scottish Parliament for Glasgow, a city she says the Nationalists have “taken for granted for years”. She believes that on Thursday, “Glasgow will give Salmond a bloody nose.” What about the Labour voters I wrote about yesterday on ConHome who have abandoned that party, and become supporters of independence, because they think this is a way to achieve socialism? Davidson agreed that “one of the really frustrating” things about the campaign had been “looking at Labour’s leaky bucket” and “knowing I’m not the person who can plug the holes”.

But she points out that Scotland “is a complex political landscape”, and the SNP has been losing supporters too: for some voters who preferred to see that party rather than Labour in power at Holyrood are nevertheless opposed to independence. Some of these people are returning to the Conservatives. Her principal assertion about Thursday is that we are about to witness a phenomenon analogous to the “shy Toryism” of the 1992 general election, when large numbers of voters supported John Major and the Conservatives without having disclosed to the pollsters that they were going to do so. This time she believes large numbers of voters will support the Union without having told the pollsters.

Davidson is warmly appreciative of the role Alistair Darling and other Labour figures including Frank Roy, MP for Motherwell and Wishaw, have played in running the No campaign, soaking up enormous amounts of pressure. She has also enjoyed campaigning alongside George Galloway, and quotes with laughter some of his best lines, such as “Farage and Salmond are two cheeks of the same arse”.

But she thinks one of the “completely secondary” benefits of the campaign is that it has given the Scottish Conservatives the chance to stand up for a cause they believe in, but one that is shared far beyond Conservative ranks: a point she made when interviewed for ConHome in January.

During the campaign, the  party has gained more volunteers, more activists and more donors. It has been able to speak to large numbers of people who had never had any kind of involvement with the Conservatives: “I think this is only healthy for our party.”

The No campaign’s street stall in Coldstream, consisting of a Union Jack attached to a plastic table bearing a selection of No campaign leaflets, is set up on the pavement outside Coldstream Parish Church, on the other side of the road from the Coldstream Guards Shop. Journalists from Belgium, Spain and France were busy interviewing Davidson, and photographing her standing next to a poster which says “UK OK”. Separatism is a big subject in various parts of Europe and the result in Scotland will be keenly watched.

In the handsome old town of Coldstream it feels easy to be at one and the same time proudly Scottish and proudly British. Coldstream stands in the vast, rural and sublimely beautiful Berwickshire, Roxburgh and Selkirk parliamentary constituency, where the Conservative candidate, John Lamont MSP, has hopes of unseating Michael Moore, the incumbent Liberal Democrat, at the general election.

Could it be that the fight to save the Union, if it ends in victory, will help us to appreciate the value of what we already have? Jock Law, who used to be an independent local councillor, passed by the stall. He pointed out that if there were ever a border post at the bridge, set up in order to prevent illegal immigrants entering by way of Scotland into England, there would be queues of traffic all through the town. And he wondered what would happen to the annual procession, in which last year 360 riders and their horses took part, from Coldstream to the site of the Battle of Flodden, four miles away in England?Would 360 passports have to be examined, to make sure that all of them had the right to enter England? Even to ask such questions seems ridiculous.

Davidson said of the referendum:  “I really care about this. Someone’s wanting to take my country away from me. If I woke up on 19th September and thought I could have done more, I’d never forgive myself.”

In Coldstream, no mobs of Yes supporters attempt to drown out the No campaign. On one side of the town stands the Hirsel, home to Sir Alec Douglas-Home, most modest and best-mannered of all Tory Prime Ministers. Here it seems natural to believe that the more modest and better mannered of the two campaigns will be victorious on Thursday. Shy Unionists can after all vanquish brash Nationalists.