Labour branded the Government's Work Programme a "failure" on Monday, as it published new figures showing that the number of people out of work for over two years has more than doubled since the general election.
The coalition's flagship employment programme was failing to get to grips with Britain's long-term jobs "crisis", said the Opposition.
Labour added that the proportion of people out of work for over a year - eligible for the Work Programme - coming off benefits and into work has halved in the last year.
Labour said that in January the Department for Work and Pensions had "dramatically" revised up its predictions for the numbers going through the Work Programme in the five years of operation by 35% to 3.27million.
"Amidst industry rumours that DWP are set to be forced to revise these projections down, ministers are ignoring parliamentary deadlines and refusing to answer Labour demands to come clean," said Labour.
Liam Byrne, Labour's Shadow Work and Pensions Secretary, said: "This Government is utterly failing to get to grips with long-term unemployment.
"The number of people out of work for more than two years - the very people the Work Programme should be helping - has more than doubled since the general election, and the rate that those out of work for more than a year are coming off benefits has halved in the last 12 months.
"Ministers have got to stop hiding and come clean. They should release all performance data for the Work Programme, admit that their scheme is failing and urgently make clear how they plan to fix this mess."