A MEDIUM security prison has been forced to house dangerous inmates because of delays over transfers to secure mental units.

Overcrowding at HMP Lewes is also forcing one in three prisoners to share a cell and use toilet facilities without any privacy.

The situation was revealed as the category B prison's independent monitoring board released the figures in its annual report this week, in which it called for the criminal justice minister Baroness Patricia Scotland to address the issue.

On four occasions between January 2005 and January 2006, the jail had three prisoners waiting more than three months to a move to one of the mental health units.

A Home Office spokesman said: "There is pressure on the whole prison system and we have worked to increase capacity. An extra 4,000 places have been created in the past two years and another 1,000 will be available by the end of 2007."

He said the measures would help the situation at HMP Lewes, although they had not been made with the prison in mind.

The Sussex Partnership NHS Trust, responsible for mental health services in Sussex, said it had long-term intentions to increase capacity at its medium-secure mental unit in Hailsham but would not be able to expand for at least two years.

The monitoring board said overcrowding was a setback for the Victorian prison's decency agenda. In many cases, pairs of inmates have been sharing one-person cells with toilets with no screens for privacy.

The prison held 541 inmates in November - 83 more than its recommended capacity. In January, 31 per cent of its one-person cells were occupied by two prisoners. Three years earlier, the figure was less than 20 per cent.

The board said the overcrowding was also damaging attempts to allow prisoners to rebuild family ties before being released.

In most cases, inmates are moved to a jail close to their home in the last period of their sentence so they can re-establish relationships in preparation for their release.

Many prisoners from around Sussex are currently being denied that chance because HMP Lewes cannot accommodate them.

In the report, the board made clear its disappointment funds were denied for a new wing at the 153-year-old prison, which would have included a gym, chapel and workshops.

It said the current gym had been in disrepair since the Sixties and the chapel was on the third floor and impossible for disabled prisoners to access.