A minister has called on Gordon Brown to consider increasing the taxation of high earners to protect the middle classes, in a move that on Sunday threatened to provoke fresh feuding within the Labour ranks.

The renewed pressure on the prime minister came as David Cameron tried to capitalise on his party’s 20-point opinion poll lead by seeking to assume the mantle of Margaret Thatcher as a reforming Conservative leader. In a series of interviews for a new book, Cameron on Cameron, the Tory leader claimed: “I am going to be as radical a social reformer as Mrs Thatcher was an economic reformer.”