The early release scheme for prisoners was stopped in April this year
The 20 most overcrowded jails in England and Wales have been revealed by prison reform campaigners.
The Howard League for Penal Reform said Kennet prison in Liverpool, with a prison population of 338, topped the list at 193% capacity.
It was followed by Preston and Swansea prisons, both at 172% capacity based on government figures for March.
The Prison Service said 1,750 extra jail places had been provided in 2009, and more than 7,500 since April 2007.
The Howard League said the prison population had reached a record high of 85,086 since the end of the early release scheme, which allowed some inmates to be let out up to 18 days early until 9 April this year.
MOST OVERCROWDED PRISONS
1. Kennet (Liverpool) 193.0%
2. Preston, Swansea 172.2%
3. Exeter 170.1%
4. Dorchester 168.0%
5. Shrewsbury 166.3%
6. Leicester 165.2%
7. Altcourse (Liverpool) 164.0%
8. Durham 161.0%
9. Canterbury 155.4%
10. Bedford 154.6%
Source: Howard League for Penal Reform, England and Wales
Prisons were at 111% capacity in England and Wales with a total of 80 prisons overpopulated, it added.
The group said problems with the implementation of an IT system for prisons meant the government had published monthly custody statistics for the first time in almost a year.
Howard League director Frances Crook said: "Overcrowding results in fewer resources being available for each individual prisoner and it results in a higher amount of prisoners per prison guard.
"Consequently, prison services focus on maintenance of basic amenities more than reintegration and security more than purposeful activity and rehabilitation."
She added: "Short-term gimmicks do not work in the long term and do not keep society safe. Politicians must act with haste to strategically reduce the prison population."
The overcrowding figure was based on the number of prisoners compared to the prison's Certified Normal Accommodation, the level of accommodation that the Prison Service aims for.
Liberal Democrat home affairs spokesman Chris Huhne said: "Tough talk from Labour and the Tories has led to record numbers of people graduating from the colleges of crime we call our prisons.
"We need to move away from the simplistic argument that prison is always the best way to reform criminals."
No comment was available from Labour or the Conservatives.