A man has been questioned by officers investigating claims of an escape plot at the jail near March, in Cambridgeshire.
Police said the man, who is 33 and comes from Bury St Edmunds, Suffolk, had been freed on police bail until 6 April.
The Prison Service said yesterday that it was unable to comment on the investigation. But it is understood that detectives are investigating reports that there was a plan to blast a hole in a wall at the prison and to lift six prisoners to freedom by helicopter.
A spokesman for Cambridgeshire Police would only say: "On March 2 this year a 33-year-old man from Bury St Edmunds was arrested in connection with an investigation into an alleged conspiracy to break out of HMP Whitemoor at March.
"The man was taken to Wisbech police station for questioning and was later released on bail pending further inquiries. He is due back at Wisbech police station on April 6."
Whitemoor, which opened in 1991, is set in an isolated part of the Fens and houses some of the UK's most dangerous prisoners in its special secure unit - a self-contained jail within a jail.
In September 1994 six inmates, including five IRA prisoners, staged a breakout from the unit. The prisoners, some of them armed, used knotted sheets to climb over a wall and were then chased across surrounding fields by police and guards before being re-captured.
An inquiry into the escape severely criticised the security regime at Whitemoor.
Eighteen months later prison officers foiled another attempted escape after a set of replica keys and home-made weapons were found inside the prison. A tip-off resulted in the discovery of two plastic key-moulds.
In April last year a prison officer was held hostage at the jail for more than seven hours by two inmates believed to have been armed with a knife.Reuse content