Mr Cable dismissed the prospect of the Lib Dems governing in a multi-party coalition alongside the SNP.

He told The Guardian: “It’s virtually inconceivable that you can have a coalition with a party that is committed to breaking up your country. We just don’t see how it could happen.”

The Lib Dems have announced that the Budget will include a package of measures to support mental health, but Mr Cable stressed that he did not expect a “bonanza” in next week’s statement by the Chancellor.

“This Budget, I think there is a common agreement across the coalition, cannot be some kind of pre-election bonanza because that would completely undermine credibility,” he said.

“We are insisting it is a coalition Budget. The two predictions I would make is that it will be a coalition Budget and that it will be quite modest.”

Mr Cable’s comments on Nicola Sturgeon’s party indicate a hardening of the Business Secretary’s stance from last month, when he indicated he was “perfectly happy to work with the SNP”, and a rainbow coalition involving the Nationalists, Labour and the SNP was “possible”.

Mr Clegg has already appeared to rule out the prospect of sharing power with the SNP, saying: “In the same way that I would never dream of putting Ukip in charge of Europe, I wouldn’t put the SNP in charge of Great Britain because Ukip wants to rip the European Union apart and the SNP want to rip our country apart.”