Seventeen inmates took their own life at jails across London last year - the highest number of prison suicides for a decade, BBC London has learned.
Four inmates committed suicide at Wandsworth prison in 2007
Belmarsh and Wandsworth prisons alone had four deaths each, the figures for 2007 show.
By comparison, the death toll stood at five in 2006. In the last 10 years 104 London inmates have killed themselves.
A ministry of justice spokesperson said there was nothing to suggest population pressures were linked to suicides.
Anne Owers, HM Chief Inspector of Prisons, told the BBC the rise in suicides was "shocking".
'Struggling to cope'
In 2006, five inmates committed suicide - three in Brixton prison, south London and one suicide each in Wandsworth, south-west London, and Wormwood Scrubs, west London.
In 2007, there were four deaths each at Belmarsh prison, south-east London, and Wandsworth, south-west London.
Three inmates committed suicide at both Brixton prison and Wormwood Scrubs, two at Holloway prison, north London, and one at Pentonville prison, north London.
Almost half of these prisoners were on remand.
Ms Owers said: "If you look at those statistics it is very stark and they are pointing to prisons that are struggling to cope with the vulnerable people that they are finding inside them."
Paul Calvert's mother said the system failed her son
Gwen Calvert, whose son Paul Calvert, 40, hanged himself at Pentonville prison in 2004, said "the system failed him".
"My Paul went to prison to lose his liberty not his life," she said.
Deborah Coles, from campaign group Inquest, said that "breakdown in communication, failure to properly assess, failure to treat and failure to deal with people in crisis" led to high suicide rates.
A Ministry of Justice spokesperson said: "There is no evidence to suggest that prison population pressures is linked to suicides.
"Transfers between prisons, and more prisoners located further from home can increase distress, and overcrowding hinders efforts to support at-risk prisoners.
"It is likely that a much greater impact is the high proportion of prisoners arriving in prison with known factors that increase the risk of them harming themselves."
The spokesperson added that an updated prisoner suicide prevention strategy would be implemented in every prison by the end of April.
The nationwide figures will be published on Wednesday.