The study warns that the number of inmates kept in cramped jails with inadequate resources has reached dangerous levels.
The prison population, which is responding to the Government's greater emphasis on locking up criminals, has increased by more than 12 per cent in the past year. About 48,500 people, over 1,000 more than places available, are currently being held in prisons and police cells, compared to 42,882 in February 1993.
Victorian built city-centre based local prisons are taking the brunt of the rises, according to the report, Prison Overcrowding - Recent Developments, by the National Association for the Care and Resettlement of Offenders.
Leicester jail tops the league table of overcrowding, with 344 prisoners in accommodation designed for 194 - an overfill of 77 per cent. Shrewsbury was second, with 71 per cent overcrowding. Nationally, nearly 8,000 prisoners are held two or three to a cell designed for one person. The number of inmates on remand has risen by 20 per cent. The report says: 'By increasing tension and frustration among those forced to live cheek by jowl in cramped conditions, overcrowding increases the risk of prison riots.'
The 11 most overcrowded jails on 31 March were: Leicester, which had 344 prisoners in accommodation designed for 194 (77 per cent overcrowding); Shrewsbury: 288 for 168 places (71 per cent); Chelmsford: 365 for 217 (68 per cent); Durham: 534 for 351 (52 per cent); Lincoln: 659 for 444 (48 per cent); Bedford: 295 for 200 (48 per cent); Hull: 430 for 295 (46 per cent); Dorchester: 169 for 118 (43 per cent); Wormwood Scrubs: 668 for 472 (42 per cent); Cardiff: 341 for 243 (40 per cent); and Leeds: 1,156 for 826 (40 per cent). Exeter, Liverpool, Birmingham, Preston and Lewes jails were more than 30 per cent overcrowded.