Male prison assaults 'rise by a third' in London
The number of reported assaults in London's male prisons has risen by a third over the last four years, BBC London has learned.
A freedom of information (FOI) request to the Ministry of Justice (MoJ) revealed there were 1,950 reported assaults in eight male prisons in 2011, up from 1,463 in 2007.
The government said it had a "zero tolerance" approach to prison violence.
A penal reform group claims a reduction of prison officers is to blame.
Shadow Justice Minister Sadiq Khan said he feared the figures were "the tip of the iceberg".
A MoJ spokesman said: "The rise in the number of assaults in London prisons is mainly due to an increase in the number of prisoners in London."
But the figures show London's male prison population grew by just 6% in the time assaults rose by 33%.
The prisons are Belmarsh, Brixton, Coldingley, Feltham, High Down, Pentonville, Wandsworth and Wormwood Scrubs.
HMP Isis, HMP Thameside and HMP Latchmere House are not included in the figures because they either opened or closed after 2007.
The number of reported assaults in the capital's female prisons fell marginally from 399 incidents in 2007 to 346 in 2011.
Mr Khan said: "The figures that the BBC has uncovered are showing an increase by a third in the numbers of assault over the last four years.
"My fear is it's the tip of an iceberg, my fear is there are many, many more assaults taking place but they're not being reported and that's not good for anybody."
Figures from the MoJ show a fall in the number of prison officers in London's prisons from 3,250 in 2010 to 3,057 in August 2012.
Frances Crook, chief executive of the Howard League for Penal Reform, said a reduction in the number of prison officers was putting prisoners and staff at risk.
She said: "There will be more deaths, there will be more violence and of course the public will suffer the consequences when people are released from prisons that are failing so badly and are such violent places.
Former prisoner Aaron French said he had witnessed violence while doing a cleaning job at Feltham Young Offenders Institution, Wormwood Scrubs and Pentonville Prison.
He said: "Me and about six other guys, we spent our days going round prison cleaning up mess, cleaning up the blood spills, suicides, sex offenders being burnt with kettle water and sugar and things like that."
He said he had noticed a reduction in prison officers and felt it was partly responsible for an increase in violence.
He said: "When there is no staff, we're banged up, even if you're meant to be going to art or a gym course or some behavioural courses that they ask us to do. If you can't do these things you're behind your door 23 hours a day.
"Two to three days this might last for and then you might get time out yourself and then another three days behind your door because there's no staff.
"And then things are finally back to normal and you're vexed. You've got itchy feet, this hasn't gone right for you and then someone says the wrong words and you're back to square one."