The 20 most overcrowded jails in England and Wales have been named by penal reformers - with Shrewsbury topping the list.
Juliet Lyon, director of the Prison Reform Trust, accused ministers of being complacent as the charity pinpointed Shrewsbury jail as the most over-subscribed jail.
It has 178 places in use but holds 326 inmates - which means it is running at an overcrowding rate of 183%, the charity said.
Swansea, which has 425 prisoners in 240 places, was named as the second most crowded, at 177%.
The PRT said almost two-thirds of prisons are officially overcrowded, with the system holding 10,000 more offenders than it was designed to handle.
Ms Lyon said: "In an economic downturn it defies belief that billions of pounds should be spent locking up more and more people only to turn them out of jail homeless, jobless and ready to offend again.
"The prison population is mushrooming out of control, and the government is still trying hopelessly to build its way out of a crisis. Ministers have grown complacent about jail overcrowding.
"It will take a concerted effort across government to reserve prison for those who have committed serious and violent crimes and to invest in drug treatment for addicts, mental health and social care and enforced community work for petty offenders."
Prisons minister David Hanson said: "The figures published by the Ministry of Justice and reproduced in part by the PRT do not show any prison operating beyond the safe level agreed by prisons and area managers.
"We will always provide enough prison places for the most dangerous, violent and persistent offenders."