Sources at Wandsworth Prison claim the inmate who died from “natural causes” was on the wing at the centre of the mystery virus outbreak.

A spokesman from the Prison Service today said the death of an inmate was from natural causes and was unconnected to the illness, which has infected 370 inmates and a number of staff.

However, sources claim the death happened on the new arrivals E wing – the wing which allegedly has the highest number of infected inmates.

The Prison Service has refused to confirm this but admitted public health officials have been sent in to determine the cause of the outbreak.

A source, who does not want to identified, said: “The death - which the prison service says is from natural causes – happened on E wing. This is the wing with the highest number of inmates falling ill.

“It spread so quickly, but I’m not surprised. E wing is where the inmates go when they first arrive at the prison.

“One of the first things they are given is their methadone. New inmates hold on to this in their mouths, spit it out and then sell it to other inmates so they get a ‘double hit’.

“I’m not surprised a virus has spread so fast when inmates are passing drugs, mouth-to-mouth.

“God knows where else it has spread. Prisoners move from prison to prison as well as in between courts.”

A spokesman for the prison service refused to comment further on the incident.