A man has been murdered in jail, police said.
Officers were called to Wandsworth Prison in south London at 7.35am today to reports of a male prisoner dead in a cell, Scotland Yard said.
The victim is believed to be aged in his 60s and though next of kin have been informed, formal identification has not yet taken place.
A post-mortem examination will take place in due course, a Yard spokesman said.
A man in his 40s, also a prisoner, has been arrested on suspicion of murder. He is currently in police custody.
The murder investigation is being led by Detective Chief Inspector Rebecca Reeves of the Homicide and Major Crime Command and enquiries continue, the spokesman said.
A Prison Service spokeswoman said: “An HMP Wandsworth prisoner was pronounced dead in hospital at 8.52am on Monday 4 May.
“A police investigation is ongoing, so it would be inappropriate to comment further at this stage.”
Wandsworth, a category B prison, is the largest in the UK, and can hold more than 1,800 prisoners. Alongside Liverpool, which is of similar size, it is one of the biggest prisons in Western Europe.
It was built in 1851, and the residential areas remain in the original buildings.
Since 1989, there has been extensive refurbishment and modernisation of the wings, including in-cell sanitation, privacy screens for cells occupied by more than one prisoner and the more recent installation of in-cell electricity.