London - Ronnie Biggs, the "Great Train Robber" who became Britain's best known convict, is "over the moon" about his release from prison, his son Michael said Friday.

Biggs, who celebrates his 80th birthday on Saturday, relayed his elation about his freedom to him via a spelling board, his son said.

On Thursday, Justice Secretary Jack Straw agreed to Biggs' release on compassionate grounds, following medical advice which showed that the prisoner was seriously ill and that his chances of recovery were slim.

Biggs is currently in hospital in the city of Norwich, in eastern Britain, suffering from pneumonia. After a series of strokes, he is fed through a tube and unable to eat and speak, his son said.

"He will stay in hospital, we have no immediate plans to transfer him," Michael Biggs said. "Hopefully my father will be able to make some sort of recovery," he added.

By agreeing to his release, Straw overturned an earlier decision refusing parole to the ageing prisoner.

Biggs, who spent 36 years on the run after the 1963 raid on a postal train, returned voluntary to Britain from Brazil in 2001. (dpa)