Prison league tables - a key plank of the Government's reform agenda - are unlikely to drive improvement across the crisis-hit system, a Commons report has warned.
MPs said the approach would not be a useful tool for comparing how well jails are functioning and argued that a single, overarching assessment will mask many aspects of performance.
The conclusion was delivered by the Justice Committee as it published a report on a shake-up which will see governors given far greater control and flexibility over their establishments.
Ministers unveiled a wide-ranging reform programme last year amid surging levels of violence and self-harm behind bars, with many of the changes taking effect this month.
Plans to introduce league tables are among headline new measures drawn up to improve scrutiny of prison performance.
The proposals first emerged in a major speech on prison reform by former prime minister David Cameron more than a year ago.
They were cited in a white paper launched by Justice Secretary Liz Truss in November.
She wrote: "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."
In its report, the committee said it encountered "mixed views" about the plans among witnesses.
"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," the paper said.
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 assessment 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."
In other findings, the committee said:
:: Giving governors more involvement in commissioning services in their prisons could lead to better outcomes for inmates - but it could also result in a "lack of alignment" across the estate and an increase in overall costs;
:: Complaints from prisoners could rise if greater autonomy and deregulation are not offset by minimum standards across the service;
:: Low morale among prison staff and governors could threaten the success of the overhaul;
:: The reforms are to be welcomed in principle but require greater clarity.
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."
A Ministry of Justice spokeswoman said: "We are carrying out the biggest overhaul of prisons in a generation and giving governors greater control over how their establishments are run.
"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."