One of Britain's biggest unions, and a key government backer, has pressured the government to change its direction on business

A windfall tax on the billion pound profits of oil companies would redefine Gordon Brown’s premiership and win back votes for Labour, said the leader of one of Britain’s biggest unions.

In the wake of the Crewe by-election catastrophe, Derek Simpson, joint general secretary of Unite, warned that: "It is not the differences between Gordon Brown and Tony Blair that are the problem, it is the similarities."

Speaking at the union's industrial conferences in Brighton this week, Simpson called for a change in policies of the Government to deal with inequality, housing shortages, rising fuel costs and the health service.

The union has welcomed the government’s action on agency workers which make it harder for employers to fire agency workers.

Said the union: ‘Big business has escaped without sanction from the Government for the grotesque excesses, the bonus culture, massive payouts for directors regardless of success and a lack of accountability in the financial system that caused the credit crunch. A recent study shows that the UK’s top companies are already saving £20 billion a year on tax through allowances and concessions.’

Simpson added: ‘We’ll be using our influence as Labour's biggest affiliate and its’ biggest financial supporter. Not by hysterical and destabilising threats of removing financial support but rather through persuasion and demonstrating that our policies are popular with traditional Labour voters.’