Winchester prison is one of the most over-crowded jails in the country, new statistics have revealed.

Now campaign groups like the Prison Reform Trust are warning that population levels in jails such as Winchester are becoming dangerously high, increasing the risk of rioting and violence.

The figures released by the Prison Reform Trust (PRT) show that record numbers of prisoners are now in British jails with fears rising that imminent changes to the Criminal Justice Bill could send the number spiralling even higher.

According to the latest Home Office figures, 90 of the UK's 138 prisons are officially overcrowded, and of those, Winchester, along with Preston, Shrewsbury, Leicester, Exeter, Dorchester, Cardiff, Swansea, Canterbury and Leeds are the worst.

Currently some 73,379 people are in prison, though the changes to the Criminal Justice Bill - currently in its second reading in the House of Lords - could add a further 14,000 to that number by the end of this decade.

Statistics show that in the last ten years inmate numbers have soared by 25,000 though new prison places have grown by only 18,000. That leaves some 17,000 prisoners "doubling up'' in cells designed for just one. The PRT notes that prisons are also not effective at stopping repeat convictions, with 59 per cent of inmates re-offending within two years of release.

Now the PRT is calling on the government to take radical steps to curb prisoner numbers. The director of the Prison Reform Trust, Juliet Lyon, said: "Prison overcrowding is at crisis point, putting intolerable pressure on prison staff, harming resettlement hopes for prisoners, damaging family ties and threatening public safety.

"The Prison Reform Trust calls on government not to wait for the next suicide or disturbance in jail, but to act now to reduce prison numbers."

Mr Gomersall said: "It is a problem for a small prison like Winchester. It means staff have to work harder as they are dealing with more people more quickly.''

But Mr Gomersall said there was no evidence that the overcrowding would lead to a repeat of the disorder in the jail seen in the late 1980s and early 1990s.