Liz Truss, the Justice Secretary, has suffered a fresh blow to her authority after a Commons report said her plans for prison league tables should be dropped.
The Justice Committee said league tables were “not a useful means” to assess prison performance and would “mask” problems within jails.
Ms Truss is already facing calls to be stripped of her second role as Lord Chancellor after concerns about the performance of her department.
In recent weeks she has also been accused by the Lord Chief Justice of “misleading” the public over rape trials, while the President of Supreme Court said she had failed in a duty to defend the judiciary.
The latest criticism came in a parliamentary report that reviewed Government proposals for improving prison performance.
The idea of league tables for prisons was first mooted by the then prime minister David Cameron in a speech more than a year ago, before being adopted as policy by Ms Truss in a white paper in November.
A single overarching assessment of prison performance will mask many aspects of performance.
She said at the time: "We will publish league tables to show which prisons are making real progress in getting offenders off drugs and developing the education and skills they need to get work."
Changes which include giving prison governors far greater autonomy - some of which come into force this month - are intended to address surging levels of violence and self-harm behind bars.
In its report, the committee said it encountered "mixed views" about the plans among witnesses who gave evidence to it.
It said: “In particular, there was some scepticism about the purpose of this approach in a prison context, where there is no consumer; about their value in driving governor performance, and about the meaning that can be attached to a single measure of performance.”
MPs concluded that league tables, as they were conceived in the white paper, are "not a useful means to compare prison performance or drive improvement".
The report said: "A single overarching assessment of prison performance will mask many aspects of performance.
"In our view it is more important that the Ministry seeks to understand more fully the factors underpinning poor and high performance and uses the learning to devise lessons to improve practice which are disseminated transparently across the estate."
The MPs said they would prefer to see the Ministry publish performance data rather than league tables.
The committee also said that low morale among prison staff and governors could threaten the success of the programme.
Conservative MP Bob Neill, chairman of the committee, said: "Governor empowerment and changes to prison performance are central to the Government's prison reform programme, which it describes as the biggest overhaul in a generation - but the lack of clarity about how some of these reforms will work in practice remains a cause for concern."
From this month, the Ministry of Justice takes responsibility for prisons commissioning and policy, while the new HM Prison and Probation Service is responsible for the operational management of prisons.
The committee said: “It is not clear to us what will happen in cases of poor performance, and how accountability will be attributed.”
A Ministry of Justice spokeswoman said: "We welcome this report which supports governor empowerment.
"We recognise that all prisons are different and that is why we are continuing to work closely with governors and staff to ensure clarity on expected standards and provide ongoing advice.
"These changes, along with our work to boost safety in prisons by employing 2,500 new prison officers, will help deliver our reforms, which will cut crime and create safer communities."
A Ministry of Justice source said that league tables would give "transparency" but that improvement would be driven by three-year contracts with individual governors that set out what they were expected to achieve.