By Dominic Casciani
BBC News home affairs reporter
The report raises a number of concerns about Brixton
The drugs problem at London's Brixton prison is so bad it is undermining treatment programmes and feeding violence, the jail watchdog has warned.
England and Wales' chief inspector said more than half of inmates felt unsafe in the "vermin-infested" prison.
Anne Owers said it "exemplifies all the problems" of overcrowding and had serious problems with gang culture.
Officials say the prison, built in Victorian times, has managed to cut the amount of drugs getting inside.
In a report into the jail, based on a visit last May, Ms Owers said its problems included two prisoners eating and living in a cell with an unscreened toilet no more than an arm's length away.
"A visit to the top landings of Brixton's old wings would quickly dispel any notion that our prisons are cushy," said Ms Owers.
"At the time of this inspection, those problems were exacerbated by the evident availability of drugs within the prison, undermining effective drug treatment and feeding violence and gang cultures."
Seven inmates had committed suicide since 2006 and there had been almost 50 incidents of self-harm in February and March 2008, she reported.
Five incidents were attempts by prisoners to hang themselves.
Despite the criticisms, Ms Owers praised a "new and energetic" management who were starting to put new systems in place.
Staff relations with prisoners were generally good and education had improved for the third of inmates who had classes, she said.
"There are things that can and must be managed better - in particular, the supply of drugs, which requires effective internal management and support from both police and prison security services.
"However, it is hard to see how Brixton, given its physical limitations, can be transformed into an effective local prison, offering both decency and rehabilitation to its 800 prisoners."
"Those responsible for offender management need to decide what role Brixton can and should play."
Phil Wheatley, head of the National Offender Management Service for England and Wales, said: "Like many local prisons of a similar age and design, Brixton presents a challenging physical environment, but staff work extremely hard within these conditions to maintain cleanliness, and to provide as extensive a regime as possible.
"The last six months have seen efforts to control the level of drug availability in the prison rewarded, with improved security and search procedures producing a significant drop in positive drug tests.
"Brixton is working to target and disrupt negative behaviours in relation to gangs and violence."
But Juliet Lyon of the Prison Reform Trust said: "This [prison] is a recipe for disaster and a terrible misuse of public funds, producing as it does a conveyor belt of revolving-door prisoners.
"At a time when everyone is short of money, Brixton makes the case for a massive switch of funds from custody to effective community penalties."