WHEN the results start tumbling in next Friday morning, after one of the oddest and most contrived general elections of modern times, every party will rush to claim victory of a kind. In spin rooms and TV studios, politicians will trumpet every scrap of positive news for their own side while magnifying their opponents’ every hiccup. They could be standing, like characters from a Samuel Beckett play, waist deep in the ashes of their own dreams, and still yammer on about what a glorious and uplifting night it’s been.

Given the high degree of nonsense on such occasions, it’s worth considering how success and failure in the election in Scotland might be judged more reasonably. Regardless of the big picture, the Unionist parties are guaranteed to agree on one thing. That any loss of seats or vote share for the SNP amounts to them losing the election and therefore a humbled Nicola Sturgeon must drop her plans for a second independence referendum.

Luckily, Scottish election history offers many jaw-dropping examples of what genuine failure looks like. When the SNP went from 11 MPs to two in 1979, that was a failure. When the Tories lost all 11 MPs in 1997, that was a proper failure. When the LibDems lost 11 of their 16 MSPs in 2011 and 10 of their 11 MPs in 2015, those were failures. And when Labour went from 41 MPs to one in 2015 that was a big, fat unambiguous disaster.

Polls suggest the SNP will lose six to a dozen seats and a chunk of vote share, but none predicts failure on anything like that scale. The party starts, after all, at a remarkable high water mark. It took 50 per cent of the vote in 2015 and won 56 seats. More SNP MPs were elected in a single night than in the party’s previous 80-year history. There’s nowhere to go but down.

Would half a dozen losses be reckoned a failure? I think the party would count that as a good night in the circumstances, although the possible loss of deputy Angus Robertson in Moray could make the pain feel sharper. If the result is worse, there are a couple of benchmarks the SNP will be particularly glad to avoid.

The party’s worst electoral reversal since 1979 was the 2003 Holyrood election, when John Swinney lost eight of 35 MSPs. If Nicola Sturgeon lost an unlucky 13 MPs, it would be a bigger percentage fall. So watch to see if the SNP go below 44 MPs, because that would mean the First Minister suffering the biggest reversal for an SNP leader in almost 40 years.

On vote share, 40 per cent is the key psychological threshold. We know how much it matters because Ms Sturgeon’s predecessor, Alex Salmond, recently boasted that since 2007 “there hasn't been a single general election poll showing the SNP below 40 per cent.”

If either of these barriers is breached, then the SNP, even if it wins a comfortable majority of seats, will have great difficulty claiming popular support for a second referendum. It won’t be a failure on the scale of some historic drubbings, but they will have gone backwards enough to put their mission in grave doubt.

As to the other parties, any LibDem gain will be scored a triumph, but they will be disappointed if they fail to add three MPs to their current one. Labour will be delighted to hold Edinburgh South and delirious to gain East Lothian. While the Tories, who have stopped making giddy claims about 15 wins, will be chuffed to get six or seven MPs against a backdrop of Theresa May imploding south of the border, although it would be far shy of their early hopes.

What will it mean for a second referendum? The arithmetic can only tell us whose fortunes are on the rise and on the wane. We’ll still be arguing about the politics come Christmas.