The BBC's Daniela Relph: "A shortage of resources means prisoners are being locked in their cells for 23 hours a day"

After a two-hour visit to the prison, Mr Boateng said more temporary staff and agency nurses would be drafted in.

"I'm satisfied that there have been deficiencies which simply are not acceptable," he said.

He said healthcare reforms in prisons were already under way, adding the situation at Brixton was "simply not tolerable".

In the last four weeks, 21 Brixton inmates have tried to kill or seriously injure themselves.

The governor, Robert Chapman, had warned that someone could die if healthcare facilities in the jail are not improved. He wrote to the Prison Service, threatening to refuse to accept prisoners with mental illnesses unless immediate action was taken.

Overcrowding and a lack of staff trained to deal with disturbed inmates are said to be at the root of the prison's problems.

Paul Boateng: Emergency visit

Staff are no longer able to cope with the number of prisoners who have mental illnesses or who need treatment for drug abuse.

In his letter, Mr Chapman said the situation was now so severe that bandages and dressings were not being changed and inmates with severe mental illness were being locked up for 23 hours a day.

"I feel we are in a no-win situation. We have no control over the numbers of prisoners requiring medical treatment entering the establishment, and yet if a tragedy occurs no one will thank us for having soldiered on in an impossible situation," he said.

Simon Milton of the Prison Officers' Association: "We are reaching a crisis point"

Simon Milton, of the Brixton Prison Officers' Association, told the BBC: "We are reaching a crisis point as far as attempts at suicides are concerned."

Staff were becoming demoralised, he added. "It's never very nice to go into a cell where someone is hanging from the cell bars."

Ann Norman, chairman of the The Royal College of Nursing warned agency nurses were not a long-term answer.

"Prisons need dedicated professional staff backed up by adequate resources and appropriate training if standards are to improve," she said.

The Howard League for Penal Reform said too many vulnerable people were being locked up.

Spokeswoman Frances Cook said: "Prisons are crammed full of people who could be dealt with in the community or who have special needs that should be catered for in hospitals."

The National Association for the Care and Resettlement of Offenders (Nacro) said improvements in healthcare at Brixton would fail unless overcrowding there was eased.