Swansea prison is Wales's most overcrowded jail and one of the top five most densely-populated in Britain.

A survey of the prison numbers released on Thursday revealed that HMP Swansea was holding 145 more inmates than the 219 it should be accommodating.

Prisons across the UK need updating

Research by the pressure group the Howard League for Penal Reform said that nearly two-thirds of Britain's prisoners were being held in overcrowded jails.

It estimated that 52,500 people were in jails running above capacity - with some buildings holding almost double the number of recommended inmates.

The latest revelation is another blow for Swansea prison - a category B establishment, built in 1861 - which has suffered a series of criticisms in recent months.

In April, an inspector's report called for urgent attention to the prison's B wing to avoid it collapsing.

It also said work should be done to improve cleanliness and sanitation, and that segregated and vulnerable patients in an underground part of the prison should be provided with toilets.

Although the hard work of staff was recognised by the inspector, the prison is a Victorian institution struggling to meet modern standards.

Our prisons are becoming no more than warehouses once again

Frances Crook, Howard League

The latest figures highlighting overcrowding will renew calls for the building to be modernised or replaced.

Soaring prison numbers mean that many prisoners are doubling up in cells meant for one.

The worst prison in Britain was named as HMP Preston with 661 prisoners - but only 356 places.

Director of the Howard League, Frances Crook, has called on the government to include a compulsory limit on the prison population in the Criminal Justice Bill - due to be published later this year.

"Our prisons are becoming no more than warehouses once again," she said.

"The consequences of overcrowding are jeopardising both the safe running of the prison system and the rehabilitation of individual offenders.

"If prison is to serve any useful purpose it must be to return prisoners to the community better equipped to lead crime-free lives.

"The current crisis effectively precludes this."

Population rise

The prison population currently stands at 71,471 and is beginning to climb after a drop of several hundred earlier in the summer.

This rise goes against the normal summer-time pattern of an overall fall in the number of inmates.

Prison numbers have spiralled from 45,500 in June 1992, and have jumped 6,000 since the start of the year.

Overall, 64 jails are now overcrowded, said the charity.

The figures are taken from the Home Office research, development and statistics directorate.

The occupancy figures relate to the number of prisoners jails were built to hold.