Prisoners are having to sleep in toilets because of overcrowding at one English jail, the chief inspector of prisons revealed today.

Inspectors uncovered the practice during an unannounced visit in February to Doncaster prison once dubbed "Doncatraz".

The chief inspector of prisons, Anne Owers, said the practice must stop.

"We were disappointed to find that two-person cells had been turned into three-person cells by placing a bed in the shared toilet. This was unacceptable," she said.

Inspectors also found "worrying" deterioration in healthcare and poor access to GPs, which they said must be urgently addressed.

Incidents of violence and self-harm have also increased.

The inspection report was published on the day the House of Commons justice committee said hasty legislation had been a "significant contributor" to prison overcrowding.

Prison numbers hit a record high of 83,000 at the end of June and Doncaster is 200 inmates over capacity.

The jail was the third prison to be privatised in the UK and is run by the Serco group. Its prisoners include young offenders aged 18-21, and adults.

Two years ago the inspectorate criticised it for "institutional meanness" after finding there were no pillows for many prisoners, or even toilet seats. Owers then branded conditions "squalid".

But the jail was praised for its resettlement work in today's report.

"Resettlement provision had continued to improve and, in the context of a busy prison with a transient local population, was among the best we have seen," Owers added.