A prisoner has been found hanging inside his cell at Wandsworth, the Prison Service has said.
Christopher Wardally, 25, was pronounced dead after he was discovered by staff at Wandsworth Prison on Friday.
Staff tried to resuscitate him, but he died at the scene.
The Prisons and Probation Ombudsman is launching an investigation into the death.
A Prison Service spokeswoman said: "Our thoughts are with family and friends.
"Christopher Wardally was found hanging by staff in his cell at 1.40pm on Friday.
"Staff and paramedics attempted to resuscitate him, but sadly he was pronounced dead at 2.18pm."
Wandsworth is the largest prison in the UK, currently able to hold 1665 prisoners.
Alongside Liverpool, which is of similar size, it is one of the largest prisons in Western Europe.
The prison was built in 1851, and the residential areas remain in the original buildings.
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