After Rutherglen, SNP and Tories' grip on power faces an existential threat – Christine Jardine

Will the 2015 nationalist tsunami now recede as quickly as it arrived in Scotland?

Well, that has put the cat among the electoral pigeons. Labour’s resounding win in Rutherglen and Hamilton West must have sent Anas Sarwar off to party conference in Liverpool with a spring in his step, confident his party’s darkest days in Scotland may be over. He will likely be greeted by widespread belief that, coupled with recent by-election success in England, the party has the momentum to sweep Rishi Sunak out of Downing Street faster than you can get from Birmingham to Manchester by train.

The result can be interpreted as evidence of the beginning of the end for two governments who have made common cause in turning each other into the enemy, at the cost of the public good. Every Labour gain in Scotland – pollsters are now predicting they could win more than the 20 Westminster seats – means an exponential improvement to their chances in a general election, and it also underlines the existential threat to the SNP.

Until that nationalist tsunami in 2015, Labour consistently held around 40 seats in Scotland. If the tide now goes back out as quickly as it came in, it may wash away with it the SNP’s hopes of another independence referendum. In a party struggling with police investigations and internal rifts, there was nothing in early pronouncements from either Humza Yousaf or Stephen Flynn to reassure the faithful that they have not lost their way. Those problems can only feel like grist to the Labour mill.

Meanwhile, Sunak seems to be doing his best to hold the door of Number 10 open for Keir Starmer, with his most recent botched attempt to harness populist appeal. The irony of a leader presenting himself as taking difficult long-term decisions for the good of the country, then scrapping a vital long-term infrastructure programme for short-term gain is overwhelming.

We need investment in our wider transport system – trains, roads, trams and buses – but not instead of a high-speed rail link, it should be as well as. With every day that has passed since Sunak’s ‘stop the train’ plan was heralded in Manchester, we learn of another aspect of the transport schemes that were said to replace it which was either already underway or, in some cases, scrapped.

More than a decade ago an engineer who worked on building the current A9 told me there had been a proposal at the time to dual the entire length, and future-proof the route. He claimed it was dismissed as too expensive. To dual it then would have been a fraction of the current cost and saved many of those lives lost on the road since. For me, Sunak’s announcement about HS2 bears all the hallmarks of the same sort of short-sightedness.

I have travelled on a high-speed train in China from Beijing to Wuhan. It travelled roughly twice the distance from Edinburgh to London in the same time. The HS2 investment would have boosted economic growth. Instead, billions have been wasted in buying land and doing engineering work which may now never be used.

The combination of Conservative incompetence and SNP decline was evident to all in a week that felt like a turning point. And not just for Labour.

Christine Jardine is Scottish Liberal Democrat MP for Edinburgh West