LABOUR must begin its conference on Sunday in a buoyant mood, but not because of the presentational mess that the Conservatives made of their HS2 u-turn.

It is the result in the Rutherglen and Hamilton West by-election that could change everything.

Before anyone gets too excited, it should be noted that one by-election does not make a landslide. There was a very low turnout in Glasgow and the unseated SNP MP was uniquely unpopular after her Covid rule breaking, but the size of Labour’s win still suggests something big could be about to happen.

Labour used to have 40-plus Scottish MPs, but it has been wiped out in Scotland so that even after the by-election triumph, it only has two. If it is to overhaul the Conservatives’ 80-seat majority in Westminster, it has to return to the old days, and its 20.4 per cent swing in Glasgow would give it 42 seats if repeated across Scotland.

Perhaps more important than the mathematics is the way the by-election answers the question about why would anyone vote SNP. After 15 years in power, they have run out of ideas of how to gain independence and their leader doesn’t seem capable of setting a new direction. Plus their former leader and her husband have been arrested, and although they were released without charge, Rishi Sunak joked in his speech that Nicola Sturgeon might be “going down” in history.

So the answer is that people no longer vote SNP. They may instead vote Labour.

Perhaps, though, the size of the swing will make Sir Keir Starmer uncomfortable. It shows how fluid, how rapidly changing, politics is nowadays. Gone are the old fashioned loyalties which once bound voters to a cause. More than ever, they now plump for whichever party looks best, which is why Boris Johnson won in 2019 ahead of Jeremy Corbyn.

Sir Keir needs to lock in the swing voters with a definite agenda rather than meekly hoping that the failings of the other parties will hand him Downing Street.