Hammond with a copy of the Tories’ 2015 manifesto, which contained a pledge he broke in his budget

Allies of Theresa May and Philip Hammond were at war last night, trading extraordinary insults over who was to blame for the budget fiasco.

Cabinet ministers revealed that Hammond had failed to warn his colleagues when he briefed them last Wednesday that raising the national insurance contributions of self-employed workers by 2p in the pound could be seen as a breach of the Conservative election manifesto.

The same national insurance (NI) rise had been rejected as political suicide by George Osborne and other chancellors as far back as Nigel Lawson in the 1980s.

A close ally of the chancellor hit back, branding Theresa May’s aides “economically illiterate” and claiming that if they had had their way the government would have slapped an even bigger NI