Ronnie Biggs, the Great Train Robber, was admitted to hospital on Saturday after complaining of chest pain
Biggs, 80, is expected to undergo tests at Barnet General Hospital later in the evening, his son Michael said.
"He had pain in his chest this morning, he's conscious but he's in a lot of pain," he said.
"He was brought in to Barnet General this morning and he'll be having tests later today.
"My daughter was born in the last few weeks so he's been in good spirits celebrating that".
Biggs, who has been living in a care home in Barnet since his release from prison in 2009 on "compassionate grounds", has been plagued with ill health in recent years.
Originally from Lambeth, south London, he was a member of a 15-strong gang which attacked the Glasgow to London mail train at Ledburn, Bucks, on August 8 1963, making off with £2.6 million.
He was given a 30-year sentence but escaped from Wandsworth prison, south London, in a furniture van after spending 15 months in jail.
He was on the run for more than 30 years, living in Spain, Australia and Brazil, before returning to the UK voluntarily in 2001.
