Official figures show that 11,900 people were remanded in custody in 2010 who were later acquitted or not proceeded against. A further 17,500 of those held in jails before trial were given non-custodial sentences.
But Nick Hardwick, Chief Inspector of Prisons, said in a new report that remand prisoners are not receiving the treatment or help they deserve.
Many had to share cells with convicts, contrary to rules, and guards did not distinguish between them.
A quarter said they felt depressed or suicidal when they were put behind bars but few were aware of support services.
They had trouble accessing phones and information about bail and many expected to have lost jobs, housing or benefits when they were finally released.
Remand prisoners also struggled to get involved in work, education or training while inside, with 29 per cent of those surveyed saying they spent all but two hours a day shut in their cells.
Mr Hardwick concluded that there should be a "comprehensive review" of remand strategies while their rights should be clarified to make sure they meet legal standards.
He said those awaiting trial should be held on separate wings to convicted criminals and prisons should have managers to ensure they receive the treatment they deserve.
Mr Hardwick said: "Despite a long-established principle that remand prisoners - who have not been convicted or sentenced by a court - have rights and entitlements not available to sentenced prisoners, we found that many had a poorer regime, less support and less preparation for release.
"This is not just a question of addressing injustice in the treatment of individuals, 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."