The way prisoners on remand are held should be changed to improve fairness and reduce costs, prison inspectors in England and Wales have said.
Nick Hardwick, the Chief Inspector of Prisons, said in a report that remand prisoners were treated less well than convicted inmates.
The rule that they should not be housed with convicted inmates was not being observed in practice, he added.
The prison service said it was addressing issues in the report.
'Shortest time'Mr Hardwick said there was a long-standing principle that remand prisoners should have rights and entitlements that were not available to convicted and sentenced prisoners.
"Yet far from being treated more favourably, this thematic review has shown that they all too often receive less support and help than convicted and sentenced prisoners," he continued.
"This is not just a question of addressing injustice in the treatment of the individuals concerned, but ensuring that costly prison places are not used unnecessarily and that everyone is given the chance to leave prison less likely to commit offences than when they arrived.
"The specific circumstances and needs of remanded prisoners need to be much more clearly and consistently recognised so that they are held in custody for the shortest time possible, and while there are given at least the same support as convicted and sentenced prisoners."
Welfare serviceThe report is based on inspection reports for 33 local prisons, fieldwork in five jails, and focus groups with remand prisoners and managers.
It found an "unresolved disjuncture" between prison rules and what happened in practice, warning that several rules have become outdated.
Inspectors found that while the Prison Rules 1999 set out legally binding entitlements for remand prisoners, appearing to suggest remand and sentenced prisoners should not be required to share a cell under any circumstances, Prison Service policy gave discretion to governors and sharing mixed cells was "the norm".
Annually between 12,000 and 13,000 prisoners are held on remand, for an average of nine weeks. Each prison place costs £40,000 a year.
Nearly a quarter of remand prisoners reported feeling depressed or suicidal when they arrived but the report said they had problems accessing welfare services.
Some remand prisoners found it difficult to maintain contact with solicitors and attend education courses.
Others were restricted from exercising their right to wear their own clothes and to vote in elections.
Acquittal ratesMore than a third said they had a drug or mental health problem and nearly half had problems obtaining bail information, the inspectors said.
The report also found almost a fifth of defendants held on remand were acquitted, and nearly a quarter were handed a non-custodial sentence.
Michael Spurr, chief executive of the National Offender Management Service, said: "This report has raised some important issues which we are addressing.
"Our existing policies recognise the distinction between remand and sentenced prisoners and set out the privileges and entitlements that reflect remand prisoners' status.
"We have already taken action to reinforce requirements on cell sharing and access to work for remand prisoners."
