'One in four' prisoners in overcrowded cells
Close to a quarter of all prisoners in England and Wales were kept in overcrowded cells in the year to April, a prison reform charity has said.
The Howard League for Penal Reform said figures showed about 19,140 inmates on average were made to share a cell designed for one person.
It said overcrowding was "far worse than anyone imagined".
The prisons minister said: "Prison is not somewhere that anyone should be comfortable about going back to."
Figures published by the Ministry of Justice show that jails held an average of just over 85,000 prisoners between April 2012 and March this year.
But the Howard League said those statistics did not state how many cells were holding more prisoners than they were designed to, and the figures it obtained via a Freedom of Information request revealed the full extent of overcrowding.
The worst-affected prison in England and Wales was said to be HMP Wandsworth, where on a typical day 835 prisoners shared cells designed for one person, which the charity also pointed out contained an open toilet.
Other prisons which held several inmates in a single cell included HMP Doncaster, where 729 prisoners were affected, and Birmingham where 670 shared.
The figures show HMP Altcourse in Liverpool and London's HMP Pentonville each had 659 inmates on average sharing cells designed for one person, while prisons in Preston, Manchester, Nottingham, Durham, and Elmley in Kent were also highlighted.
Some 777 prisoners were made to sleep three to a cell in rooms designed for two.
The 13 prisons which saw inmates sharing cells designed for two included HMP Belmarsh, HMP Altcourse and HMP Elmley.
Frances Crook, Howard League chief executive, said the "real state" of overcrowding was "far worse than anyone imagined".
She said: "It should come as little surprise that such crowded conditions leave staff hugely overstretched, especially as more are being laid off. This means there are little to no opportunities for prisoners to work, learn or take courses to turn them away from crime.
"If the Ministry of Justice is serious about reducing reoffending it must tackle overcrowding now. Successive governments have peddled the lie that you can build your way out of a prisons overcrowding problem.
"While public services are being cut, ministers should look at more effective and affordable solutions. They need to address the fact the prison population has doubled in just 20 years and move people on to community sentences."
Prisons Minister Jeremy Wright said older prisons were being replaced with newer accommodation that was cheaper to run and the government was tackling reoffending.
He added: "Let's be clear what overcrowding in prison actually means. Typically it means having to share a cell rather than have one to yourself. Prisoners are treated humanely but prison is not somewhere that anyone should be comfortable about going back to.
"All prisons have safe population levels and have capacity to take those sent there by the courts."