Downey told the court that he had been addicted to drugs since he was eight and the threat of a prison term had not stopped him using cocaine and heroin.

His lawyer Robert Shapiro had argued for mercy saying the actor was a changed man and was fighting his addictions.

But Judge Lawrence Mira said: "I don't believe your client is committed to not using drugs. You may call that addiction. But there is some level of choice.

"I don't think we have any alternative [to jail]. We have used them all."

She said the actor had manipulated doctors and psychiatrists during seven court-ordered drug rehabilitation courses, all of which he had failed to finish.

Explaining his addiction Downey told the court: "It's like I've got a shotgun in my mouth, with my finger on the trigger, and I like the taste of the gun metal."

OJ Simpson's team

Downey was jailed for three years but, taking into account the time he has served in custody, he could be free in just over a year.

He was found guilty of drugs and weapons possession in June 1996 after police stopped him for speeding and found cocaine, heroin and a pistol in his pickup truck.

Mr Shapiro assembled the same team of lawyers to represent Downey that successfully defended another Hollywood star, OJ Simpson, when he was charged with the murder of his ex-wife and her friend.

Downey won an Oscar nomination for his work in the title role in Chaplin, the 1992 screen biography of the famed comedian. His other film credits include Natural Born Killers, One Night Stand and US Marshals.