One prisoner harmed themselves every three days in Lewes Prison last year.
The Argus can reveal the shocking statistic a day after we reported the death of prisoner Gareth Russell, 25, who was found hanging in his cell early on Tuesday.
While there were no recorded suicides in the prison in 2006, staff recorded 123 self-harm incidents among 65 prisoners, including drug overdoses and attempted hangings.
In October alone, there were 25 incidents of self-harm at the institution in Brighton Road, Lewes.
The National Offender Management Service said most of the figures refer to prisoners cutting themselves.
It says the figures, obtained under the Freedom of Information Act, may be as much as 15 per cent higher than those released because of problems with record-keeping.
The incidents took place all over the prison site, including in cell blocks, the healthcare centre and even the reception area.
A number also took place in specialised units set aside for prisoners on detox programmes, new prisoners, prisoners who have been segregated from other inmates and for vulnerable prisoners.
A spokeswoman for the Prison Service said: "HMP Lewes holds a high number of prisoners with mental health issues and drug dependencies and this has an impact on the number of incidents of self-harm within the prison.
"However, HMP Lewes has a very good NHS-led mental health team, well-trained staff and all prisoners are assessed and supported upon arrival. HMP Lewes has robust methods to deal with this problem."
Will Higham, of independent charity the Prison Reform Trust, said prisons such as Lewes too often become a dumping ground for people with mental health problems.
He said: "These figures are horribly sad, and perhaps even more horribly they are not surprising.
"Self-harm in particular is linked to people on remand, and very often mentally ill people get remanded too.
"A lot of mentally ill people will have relatively chaotic lifestyles.
"If you have problems with drugs or accommodation you're more likely to end up in prison."
He said the government has failed to deliver on promises to provide psychiatric support and assessment throughout the justice system.
Prison policy at Lewes is to assess prisoners thought likely to be at risk of suicide or self-harm, reviewing each case 24 hours after concern is raised.
The system, which provides specialised training for staff, is being introduced in all prisons across the UK, with Lewes the first to bring it in.
Lewes Prison, built in 1853, holds a maximum of 558 male prisoners, both adults and young offenders on remand.
Most adult prisoners are kept in shared cells, and are either serving short-term sentences or are on remand waiting for court hearings.
Prisoners have access to literacy, numeracy, IT and social skills training, as well as employment in workshops.
Gareth Russell, an alcoholic, had been living rough in the Brighton area for some time.
He was found guilty of the manslaughter of Terry Hannaby, 34, on Thursday after a seven week trial at Hove Crown Court.
Russell was sentenced to six years for his part in the attack.
Dafydd Field, 52, who was charged with the murder of his six-year-old son Jethro, was found electrocuted in his cell at Lewes on April 10.
Emma Kelly, 31, from Heathfield, was found hanging in her cell at Send prison in Surrey on April 18.
She was eight months into a nine year sentence for supplying cocaine and heroin to her young son.
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