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Half a century after the infamous Great Train Robbery, the most notorious member of the gang, Ronnie Biggs, is unrepentant and says he is proud of his role in the heist.

The gang stole the equivalent of ??45 million ($69 million, 52 million euros) in today's money from a mail train travelling from Glasgow to London 50 years ago on Thursday.

The crime itself was audacious enough, but it was Biggs' 36 years on the run and his high-profile new life in Brazil which propelled him to fame.

He escaped from prison in 1965 and was finally arrested and thrown back in jail in 2001 on his voluntary return to Britain.

Biggs, who will celebrate his 84th birthday on the anniversary of the robbery, was released from prison in 2009 after his lawyer claimed he was close to death following a series of strokes.

But he is still alive and although now confined to a wheelchair he showed he has lost none of his old defiance by making an obscene hand gesture to journalists at the funeral of the gang's mastermind Bruce Reynolds in March this year.

Biggs, who cannot speak and communicates through a spelling board, said ahead of the 50th anniversary: "If you want to ask me if I have any regrets about being one of the train robbers, my answer is 'no!'

"I will go further: I am proud to have been one of them. I am equally happy to be described as the 'tea-boy' or 'The Brain'.

"I was there that August night and that is what counts. I am one of the few witnesses -- living or dead -- to what was 'The Crime of the Century'."

Biggs admitted however that he does have some regrets.

"It is regrettable, as I have said many times, that the train driver was injured," the Londoner said. And he was not the only victim.

"The people who paid the heaviest price for the Great Train Robbery are the families, the families of everyone involved in the Great Train Robbery, and from both sides of the track.

"All have paid a price for our collective involvement in the robbery. A very heavy price, in the case of my family.

"For that, I do have some regrets."

While the train robbers' exploits have passed into folklore, many people deplore the almost forgotten fate of the driver, Jack Mills.

He was coshed over the head by another member of the gang, never recovered from his head injuries and died seven years later.

'Big Jim' Hussey is said to have claimed on his deathbed that he was the attacker, although other accounts say it was a man who has never been brought to justice.

The driver had stopped the train at a remote bridge at Ledburn in Buckinghamshire, northwest of London, after seeing a red signal -- but it was fake, created using a glove and a battery-powered light.

Once Mills was incapacitated, the gang uncoupled the engine and the first two carriages and a human chain of robbers removed 120 sacks containing 2.5 tonnes of cash.

The crew left in the rest of the train did not realise anything had happened until it was too late.

But the plan unravelled when the gang members abandoned plans to lie low for several weeks and instead fled from the farmhouse they had rented. The police, tipped off by a neighbour, rounded up many of them.

Nine of the 16 involved went on trial in 1964 and each was given 30 years in jail, although most did not serve out the whole sentence.

Biggs escaped from London's Wandsworth prison in a furniture van 15 months later. He fled to continental Europe in a boat then underwent plastic surgery in Paris.

He spent four years on the run in Australia but fled again to Brazil in 1970. He was tracked down but could not be extradited as he had fathered a Brazilian child.

From his base in Rio de Janeiro he taunted the British police, aided by the British tabloids who lapped up his roguish tales.

When he voluntarily returned to Britain in May 2001, he was re-imprisoned before being released on compassionate grounds in 2009.

Biggs, who now lives in a nursing home, has contributed to a new book about the robbery to explain first-hand the complete story of the heist.