Great Train Robber Ronnie Biggs has been re-admitted to hospital with severe pneumonia.
His son Michael said: "It is the worst he's ever been. The doctors have just told me to rush there."
Justice Secretary Jack Straw refused to release Biggs, 79, on parole earlier this month saying he is "wholly unrepentant" about his crimes.
Ailing Biggs has been moved between his prison cell at Norwich Prison and a bed at Norfolk and Norwich University Hospital several times.
A picture of him in his hospital bed was sent to MPs by his legal adviser Giovanni Di Stefano several weeks ago.
His family said his life remains in the balance as he is suffering pneumonia and has fractures of the hip, pelvis and spine. They said Biggs has suffered three strokes and cannot eat, speak or walk.
Justice Secretary Jack Straw rejected a parole board recommendation that Biggs be released, saying he has expressed no remorse for his crimes.
Biggs, from Lambeth, south London, was a member of a 15-strong gang which attacked the Glasgow to London mail train at Ledburn, Buckinghamshire, in August 1963, and made off with £2.6 million in used banknotes.
He was given the 30-year sentence but after 15 months he escaped from Wandsworth prison in south west London by climbing a 30ft wall and fleeing in a furniture van.
Biggs was on the run for more than 30 years, living in Spain, Australia and Brazil, before returning to the UK voluntarily in 2001 in search of medical treatment.
He was locked up in Belmarsh high security prison on his return before being moved to a specialist medical unit at Norwich prison.
The decision means Biggs will not be free to celebrate his 80th birthday on 8 August - 46 years to the day since the raid.
A Ministry of Justice spokeswoman declined to comment. She said: "We do not comment on individual cases."Reuse content