Gordon Brown attempted to exploit his newfound political strength last night by attacking the SNP’s core belief, saying bluntly that an independent Scotland could not have bailed out the country’s stricken banks.

The Prime Minister said that the United Kingdom’s financial strength made a £37 billion capital injection possible for the banks, including the Royal Bank of Scotland and HBOS.

An emboldened Mr Brown also said that he and his wife, Sarah, planned to campaign in the Glenrothes by-election due on November 6, underlining Labour’s growing confidence. Glenrothes borders Mr Brown’s own seat of Kirkcaldy and Cowdenbeath.

It is a massive change from a few weeks ago when Labour was seen as the outsider to win the seat, where it is defending a 10,664 majority against the SNP.

The claims by its leader, Alex Salmond, that an independent Scotland could form part of a Northern European “arc of prosperity” have come under increased scrutiny after Scotland’s two leading financial institutions nearly collapsed.

Mr Brown said of the bank rescue package in an interview with BBC Scotland: “It’s the Union that makes this possible. . . When things are difficult we are in a position to support each other – stronger together, weaker apart.” He said the banks would be rebuilt “over time” to preserve the banking legacy of Scottish financial institutions.

While claiming this was not the time for scoring party political points, he said: “The important thing is that we were able to act decisively with £37 billion. That would not have been possible with a Scottish administration.”

The Prime Minister’s remarks came as Mr Salmond’s devolved administration was putting together a package of reflationary measures for the Scottish economy. As part of these measures, the SNP wants the Brown Government to hand over £1 billion that the Nationalists claim belongs to Scotland. It includes £120 million from the fossil-fuel levy surplus and council tax benefits worth £476 million.

Times Recommends

• One case exposes grim reality for thousands
• A glass case: Prince who yearns for action
• Elizabeth Gaskell: I won’t see out the year