An 84-year-old man has become the first British prisoner to die after contracting coronavirus.
Edwin Hillier, an inmate at HMP Littlehey - a category C male sex offenders' prison in Cambridgeshire, died in hospital on Sunday.
Hillier, a convicted paedophile, reportedly had health issues.
A second serving UK prisoner, a 66-year-old male inmate at HMP Manchester, died in hospital on Thursday after contracting coronavirus.
Former school caretaker Hillier, from Hemel Hempstead, was jailed at St Albans Crown Court in 2016 for sexually abusing two girls in the 1970s.
A HM Prison Service spokesman said: "Our thoughts are with his family at this time."
He added investigations by the Prisons and Probation Ombudsman would take place into the deaths, as is customary for deaths in custody.
As of Wednesday, 19 inmates had tested positive for Covid-19 across 10 jails and four prison staff had tested positive for the disease across four jails.
Three prisoner escort and custody services staff have also tested positive for Covid-19.
HM Prison Service said robust contingency plans had been put in place at its facilities in consultation with Public Health England and the Department of Health and Social Care.
It added that prisons are well prepared to take immediate action wherever cases or suspected cases of Covid-19 are identified, including the isolation of individuals where necessary.