Ed Miliband is facing fresh pressure from inside his own party over Labour's links to the unions after a frontbencher suggested the "parent could not live in the child's house".
Phil Wilson, a Labour whip, writes in a pamphlet published tomorrow that a "healthy Labour movement cannot be the preserve only of the public sector and remain the people's party" while "ignoring the 85 per cent of private sector employees not in a union".
Mr Wilson, the MP for Tony Blair's old seat of Sedgefield, adds: " The trade union movement gave birth to the Labour Party. After one hundred years, it's now time to allow the child to move on. Both unions and party need the confidence to understand: if the parent did not live in the child's house the bond between both could still be strong.
The pamphlet, entitled All the Pits Have Closed, is being launched by Mr Miliband's policy chief, Jon Cruddas. Mr Miliband is under pressure to make a symbolic break with the unions, particularly with the giant super-union Unite, which bankrolls the cash-strapped party, to broaden Labour's appeal.
Yet the Labour leader backtracked last year on a promise to weaken the union bloc vote at conference and is resisting further reform, despite Unite's strike threat during the Olympics.