Straw last month rejected Biggs's application for parole on the grounds that the robber was "wholly unrepentant" about his crimes, but he said the decision on compassionate release was based on "different considerations."
"The medical evidence clearly shows that Mr Biggs is very ill and that his condition has deteriorated recently, culminating in his re-admission to hospital. His condition is not expected to improve," Straw said.
Michael Biggs, who had campaigned for his father's release, said Biggs was delighted by the government's decision.
"I've just been able to spend some time with my father... He is over the moon," he said outside the hospital late Thursday, adding that his father had used a spelling board to give his reaction.
"I am delighted that common sense has finally prevailed and that the government saw that it was absolutely unneccessary to keep my father in prison," he said.
"Practically he'll still be staying in hospital but it's the feeling that not only my father but the family will have that it's finished, and he will be able to die with some dignity. He will able to die as a free man," he added.
Biggs said earlier that he hoped his father would live long enough to see his 80th birthday on Saturday -- 46 years to the day since the heist.
The so-called Great Train Robbery saw a 15-strong gang hold up a London to Glasgow mail train and make off with 2.6 million pounds, a huge sum at the time, at a railway bridge north of London.
Most of the cash was never found. The train driver, Jack Mills, was hit on the head during the robbery and died seven years later without ever making a full recovery.
Biggs played a minor role in the hold-up but was jailed for 30 years in 1964. He subsequently escaped by scaling a prison wall and jumping onto the roof of a furniture van.
On the run for decades, he fled to France, where he had plastic surgery, and Spain before heading to Australia. But he eventually settled in Brazil, where he was often pictured partying in British newspapers.
Detectives travelled to Brazil in 1974 in the hope of catching him, but they were thwarted because Biggs by then had his son, Michael, with his Brazilian girlfriend, making him legally untouchable.
He nevertheless handed himself over to the British authorities in 2001 amid a blaze of publicity. Biggs said his last wish was to enjoy a pint of beer in an English pub by the seaside before he died, but he was sent back to jail.
Michael Biggs said his father had exressed regret "several times" for the crimes that he committed.
"(But) my father is not sorry for the life he led, because had he not led this life he wouldn't have me as a son or my daugher as a grand child."
His lawyer Giovanni Di Stefano said Biggs was unlikely to leave hospital.
"He is being released effectively to die and that cannot be considered a victory. But it's a victory for common sense and Mr Straw has made the right decision," he told Sky News.
If his condition was to improve, Biggs would be transferred to a nursing home in Barnet, north London, near his son's home.
The three prison service staff watching Biggs in hospital will be withdrawn on Friday, once the licence for his release is finalised.
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"The medical evidence clearly shows that Mr Biggs is very ill and that his condition has deteriorated recently, culminating in his re-admission to hospital. His condition is not expected to improve," Straw said.
Michael Biggs, who had campaigned for his father's release, said Biggs was delighted by the government's decision.
"I've just been able to spend some time with my father... He is over the moon," he said outside the hospital late Thursday, adding that his father had used a spelling board to give his reaction.
"I am delighted that common sense has finally prevailed and that the government saw that it was absolutely unneccessary to keep my father in prison," he said.
"Practically he'll still be staying in hospital but it's the feeling that not only my father but the family will have that it's finished, and he will be able to die with some dignity. He will able to die as a free man," he added.
Biggs said earlier that he hoped his father would live long enough to see his 80th birthday on Saturday -- 46 years to the day since the heist.
The so-called Great Train Robbery saw a 15-strong gang hold up a London to Glasgow mail train and make off with 2.6 million pounds, a huge sum at the time, at a railway bridge north of London.
Most of the cash was never found. The train driver, Jack Mills, was hit on the head during the robbery and died seven years later without ever making a full recovery.
Biggs played a minor role in the hold-up but was jailed for 30 years in 1964. He subsequently escaped by scaling a prison wall and jumping onto the roof of a furniture van.
On the run for decades, he fled to France, where he had plastic surgery, and Spain before heading to Australia. But he eventually settled in Brazil, where he was often pictured partying in British newspapers.
Detectives travelled to Brazil in 1974 in the hope of catching him, but they were thwarted because Biggs by then had his son, Michael, with his Brazilian girlfriend, making him legally untouchable.
He nevertheless handed himself over to the British authorities in 2001 amid a blaze of publicity. Biggs said his last wish was to enjoy a pint of beer in an English pub by the seaside before he died, but he was sent back to jail.
Michael Biggs said his father had exressed regret "several times" for the crimes that he committed.
"(But) my father is not sorry for the life he led, because had he not led this life he wouldn't have me as a son or my daugher as a grand child."
His lawyer Giovanni Di Stefano said Biggs was unlikely to leave hospital.
"He is being released effectively to die and that cannot be considered a victory. But it's a victory for common sense and Mr Straw has made the right decision," he told Sky News.
If his condition was to improve, Biggs would be transferred to a nursing home in Barnet, north London, near his son's home.
The three prison service staff watching Biggs in hospital will be withdrawn on Friday, once the licence for his release is finalised.
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