It comes after a leading think tank projected that Labour are set to oversee the second-worst levels of household income growth on record – behind only the previous Tory government.

The SNP Westminster leader, who will run for Holyrood in 2026, said the foundations of the UK “can’t and won’t be fixed”, accusing successive Westminster governments of delivering the “same pattern of painful policies” in every Budget for 15 years.

Flynn’s comments come after the Resolution Foundation, in its analysis of the UK Labour Budget, warned that the spending plans were set to bring in cuts only 12 percentage points short of the height of austerity.

“If the Government raises defence spending to its stated goal of 3.5% of GDP by 2035, health spending grows at its long-run average, and education spending is held flat in real per-pupil terms, then today’s announcements imply cutting ‘other’ departments (including local government and justice) by £6.4 billion in real terms between 2028-29 and 2029-30,” it said.

“Cuts of this nature would be equivalent to 88% of the average annual cuts made during the peak austerity years (2009-10 to 2018-19).”

The foundation further analysed real household disposable income (RHDI) – the UK Government’s preferred measure of living standards – and found that it is “forecast to have grown by 0.5% a year on average (or £740 in total) by the end of the Parliament”.

“This would be an improvement on the negative growth of the last Parliament, but it would still be the second worst Parliament for income growth on record,” the think tank said.

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Elsewhere, the Office for Budget Responsibility (OBR) forecast on Wednesday that growth in disposable income would drop from 3% in 2024-25 to just 0.25% by the end of the decade, owing to tax changes announced by Rachel Reeves in the Budget.

Flynn told the Press Association: “This UK Budget again exposes the depth of damage and decline that Westminster has inflicted on people’s lives for a generation.

“The brokenness of Brexit Britain has been laid bare and is now locked in – every budget and every year sees the same pattern of painful policies that have hit people in the pocket for over 15 years.

“That was the toxic legacy of the Tories, but now the official figures confirm that the United Kingdom is set for another lost decade under the Labour Party.

“A generation of Scottish people have now lived through Brexit Britain – a place that is poorer and smaller, with a Farage future the only thing on the Westminster horizon.

“That reality has clear constitutional consequences – the economic case for the United Kingdom has been torn apart by flatlining living standards, falling growth, and constant chaos with Westminster.”

Chancellor Rachel Reeves outside 11 Downing Street before delivering her Budget on Wednesday (Image: James Manning)

Flynn said politicians at Westminster have been “promising change”, while things “have gone from bad to worse”.

He added: “A new generation in Scotland desperately deserves a fresh start and a fresh choice.

“We know Westminster’s past all too well, we know the damage it is inflicting in our present – this can be the moment where we determine that another generation of Scots won’t be forced to live with Westminster’s future.

“That is the opportunity that the SNP offers – by winning a majority next May we can unite and break beyond the brokenness of Britain and give people the hope of a fresh start with independence.”

Flynn has urged voters in Scotland to back his party in May in the hopes of securing a majority at Holyrood and a subsequent referendum on Scottish independence.

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But the Chancellor told BBC Radio Scotland on Thursday the UK Government will not allow another referendum, regardless of the outcome of next year’s election.

Speaking on BBC Radio Scotland on Thursday, the Chancellor said: “I can be very clear there won’t be another referendum.

“When there was a referendum just a few years ago, it said that this was a once in a generation referendum. People gave their verdict.

“Then we don’t need another one. And the Scottish Government, whoever is in charge, should focus on the priorities of the Scottish people – bringing down NHS waiting lists, which are still far too high in Scotland, improving educational outcomes for people in Scotland and investing in infrastructure.”

After Reeves’s Budget, Flynn predicted it would be the last delivered by a government led by her and Keir Starmer.