An inquiry has begun into allegations that a prisoner had sex with his wife when they were left alone in a shower room while he was a hospital patient.
An anonymous letter was sent to a local newspaper by a nurse at the West Suffolk Hospital in Bury St Edmunds outlining the allegations.
It was also sent to the governor of Edmunds Hill jail at Stradishall, which houses category C prisoners.
A Prison Service spokeswoman confirmed on Friday an investigation had begun.
She said: "We can confirm that there is an internal investigation at HMP Edmunds Hill into an alleged incident during an escort at an outside hospital."
A spokesman for the hospital said: "The conduct of prisoners while in the hospital is solely the responsibility of prison guards.
"Staff will support that investigation in every way possible."
It is believed the alleged incident took place last month.
