Gordon Brown’s last Budget as chancellor came back to haunt him on Wednesday, as the Conservatives warned that 5m poorer households were about to be hit by the abolition of the 10p income tax band, which takes effect on April 6.

Labour MPs are increasingly fretful over the tax change, announced by Mr Brown in 2007, fearing it will hit the party’s core voters at a time when they are already struggling with higher bills for food, fuel and council tax.