Michael Biggs said he had never seen his father so seriously ill
The Great Train Robber Ronnie Biggs has been readmitted to hospital in Norfolk with severe pneumonia.
The 79-year-old inmate at Norwich Prison has been taken to the Norfolk and Norwich University Hospital.
He was taken to the hospital last month with a serious chest infection and a fractured hip but returned to prison on 17 July.
His son Michael Biggs said: "It's the worst he's ever been. The doctors have just told me to rush there."
Earlier this month, Justice Secretary Jack Straw refused a parole application by Biggs, who he said remained "wholly unrepentant" for his crimes.
He has been moved between his prison cell and a bed at the hospital several times.
Ronnie Biggs in a hospital bed in Norwich last month
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 remained in the balance as he was suffering pneumonia and has fractures of the hip, pelvis and spine.
They said Biggs has had three strokes and cannot eat, speak or walk.
A parole board recommended he be released but Mr Straw disagreed, saying he had 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 as it passed through Buckinghamshire in August 1963 and made off with £2.6m in used banknotes.
He was given a 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.
He was on the run for more than 30 years, living in Spain, Australia and Brazil, before returning to the UK voluntarily in 2001.
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