Gordon Brown was on Friday warned by Britain’s top trade unionist that he was facing a new onslaught from the Labour left unless he took on the “super-rich” and reined in his government’s close relationship with the City and big business.

Brendan Barber, head of the Trades Union Congress, called on Mr Brown to ignore “intimidation” from the City and to levy a windfall tax on energy companies, as well as to make the very wealthy pay more in tax.