James Earl Ray is being questioned by police after he was arrested by Scotland Yard officers at Heathrow Airport as he tried to board a flight to Brussels.
He was charged at Cannon Row police station with possessing a forged passport and having a firearm without a certificate.
The Justice Department in Washington announced it would be seeking Ray's extradition on a murder indictment brought against him on 7 May in Memphis, Tennessee.
Tight security
The British Home Secretary, James Callaghan, is expected to authorise the institution of extradition proceedings against Ray.
Tight security precautions are in place at Bow Street Magistrates' Court, where Ray is due to face the charges today.
Members of the public and press will be searched for firearms and other weapons before they are allowed to enter the court.
The FBI said Ray was an escapee from Missouri State Penitentiary, who had been on the run since 23 April 1967. He had been serving a 20-year sentence for armed robbery.
Dr King was shot on 4 April while standing on his hotel balcony in Memphis and died later in hospital.
Police quickly identified Ray as the chief suspect. He was renting a room in Memphis close to the Lorraine Motel where Martin Luther King was shot.
He had served a string of sentences for offences ranging from drunkenness in the US Army to burglary, armed robbery and forgery. He was discharged from the army in 1948.
He fled the city shortly after the shooting and was traced to Europe where he was eventually apprehended in London.
James Earl Ray
The FBI is seeking the extradition of James Earl Ray to the United States
In Context
James Earl Ray was jailed for 99 years in Memphis after admitting that he murdered Dr Luther King.
He pleaded guilty to avoid the death penalty.
FBI director Edgar Hoover said a systematic search of 53,000 fingerprints led to the determination that Eric Starvo Galt and James Earl Ray were the same man. He also used the name Ramon George Sneyd.
Ray later retracted his guilty plea and protested his innocence and by the 1990s his continued requests for a new trial gained momentum.
In 1997 Dr King's son Dexter met Ray and publicly supported him, and the next year Attorney General Janet Reno ordered a full review of the case.
That review ended in 2000 with a finding that "no credible evidence" existed to support various conspiracy theories.
Ray died in prison in 1998, aged 70.
Stories From 8 Jun
1982: Fifty die in Argentine air attack
1968: James Earl Ray quizzed over King death
1999: Liar Aitken jailed for 18 months
1963: Ward charged over 'immoral earnings'
1978: Woman takes world sailing record
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