He closed Scottish Labour’s spring conference in Dundee yesterday with a pledge to increase spending north of the Border, including the possibility of high-speed rail up to Scotland.

But opponents insisted that Labour cannot be trusted on the economy and pointed to splits within the party over Brexit.

Scottish Labour leader Richard Leonard unveiled plans to transform Scotland’s economy if he becomes First Minister during his keynote speech on Saturday, while UK leader Jeremy Corbyn told delegates on Friday that the party was “preparing to go into government” at Holyrood and Westminster.

Shadow Chancellor John McDonnell delivers the keynote speech on the final day of the Scottish Labour conference. Picture: Dave Johnston

And Mr McDonnell set out a radical spending programme yesterday with a stinging attack on the SNP’s “measly” proposals.

He claimed an extra £3 billion a year was earmarked for Scotland in Barnett consequentials – cash that comes to Scotland as a result of spending decisions taken by the UK – amounting to £30bn over ten years.

He also said Labour’s £250bn National Transformation fund would see £20bn spent in Scotland over a decade, that could help “rebuild our crumbling infrastructure and deliver key investments such as extending HS2 to Scotland”.

A UK National Investment Bank could provide another £20bn in Scotland over ten years, helping small and medium businesses.

Mr McDonnell said: “Let’s do the sums. Taken together, our commitments over a decade could mean an additional £70bn for the Scottish economy.”

And he compared the spending from Labour’s planned UK Investment bank with the SNP’s “measly £340 million” of initial capital for the “so-called Scottish Investment Bank”.

He told the Nationalists: “If you are going to steal our ideas, for goodness’ sake do it with a bit of style.”

The shadow chancellor used his speech to condemn the austerity being imposed by both the UK Conservative government and the SNP administration in Edinburgh.

Under the SNP he claimed Scotland’s economy was “stagnating”, telling party activists: “There has been nothing done in the last ten years to grow the economy, to tackle the blight of poverty that is scarring Scotland. Both north and south lives are being destroyed and millions have been left in despair, and it is thanks to the failed economic dogma of neoliberalism and austerity.

“Austerity is a political choice, it’s not an economic necessity. And the Tories and the SNP, they chose austerity. We choose the socialism, we choose the alternative.”

With Scottish Labour having elected left-winger Mr Leonard as its new leader in November, Mr McDonnell also insisted the party was heading back to power in both Westminster and Holyrood. He told the conference: “We’re coming for power and to power and we will seize it in Scotland as we will in the rest of the UK.”

The results in the 2017 general election, where Scottish Labour increased its tally of MPs from one to seven, and came second to the SNP in several other areas, had “cheered his heart”, he said.

But an SNP spokesperson said: “John McDonnell can’t be trusted on anything he says when it comes to Scotland. The shadow chancellor has said a Labour government would scrap the bedroom tax and restore housing benefit – both of which are already being mitigated by the Scottish Government, and that Labour would review Universal Credit – which the SNP Scottish Government is already doing.

“It’s Labour’s failure to commit to membership of the single market when the UK leaves the EU which is the biggest threat to the Scottish economy.”

Labour in Â£70 billion pledge to win power in Scotland