Theresa May has rejected accusations that she had broken a manifesto pledge on tax rises as she faced a growing rebellion from Tory MPs.

The Prime Minister refused to back down over the controversial rise in National Insurance contributions for the self-employed, but announced a series of concessions to buy time before the policy faces a Commons vote.

Senior Conservatives including a minister and Government whip denounced the key pillar of Philip Hammond’s Budget and said they would seek to overturn it when it comes before Parliament.

The Telegraph has learnt that the leader of the mutiny, the MP for Berwick upon Tweed Anne-Marie Trevelyan, is in the process of drafting an amendment designed to kill off the proposed increase, which has the backing of 30 Tory MPs.