POLICE killer Harry Roberts is to be released from prison, despite being warned by the judge at his trial that he would likely die in jail.

Roberts, 78, was jailed for life for the murder of three policemen in 1966, an act that was condemned by the judge as "the most heinous crime for a generation or more".

His upcoming release has sparked fury, with the Police Federation branding it a "betrayal" of the dead officers, and London mayor Boris Johnson saying the public would be "sickened".

But Deputy Prime Minister Nick Clegg defended the Parole Board decision, saying it would be a "disaster" to let emotions dictate which prisoners can be freed and when.

Roberts and two accomplices had been in a van near Wormwood Scrubs prison in London preparing for an armed robbery when he shot three unarmed officers.

Detective Sergeant Christopher Head, 30, Detective Constable David Wombwell, 25, and Constable Geoffrey Fox, 41, were killed in the attack on August 12, 1966.

At his trial, Judge Mr Justice Glyn-Jones jailed Roberts for life, with a minimum 30-year tariff. He told Roberts: "This is one of those cases in which the sentence of imprisonment for life may well be treated as meaning exactly what it says."

Roberts is now expected to leave Littlehey prison in Cambridgeshire shortly, after the Parole Board approved his release.

Last May, Home Secretary Theresa May pledged to introduce legislation to ensure life meant life for people who murder police officers. It is expected to come in next year.