A notorious police killer is to be released from prison in what has been called a "scandalous, hurtful and abhorrent decision".
Harry Roberts, 78, was jailed for life for murdering three unarmed officers in Shepherd's Bush, west London, in 1966.
They were shot after pulling over a van containing Roberts and two others, after an armed robbery.
The Metropolitan Police Federation said the decision was a "betrayal of policing" by the judicial system
It said Roberts' planned release was a "scandalous, hurtful and abhorrent decision which opens the door even further for those who have scant regard for law and order".
"Those who place their lives on the line to protect the public deserve better than this terrible outcome," it added.
BBC Home Affairs correspondent Danny Shaw said a panel of three from the Parole Board of England and Wales had approved the release.
He said the test the board applied in such cases was whether or not the prisoner continued to pose a significant risk of serious harm.
Roberts could be released from Littlehey Prison in Cambridgeshire within days, although it could take up to three weeks. He will have to adhere to strict conditions.
The murders of PC Geoffrey Fox, 41, Sgt Christopher Head, 30 and 25-year-old Det Con David Wombwell became one of the most infamous crimes of the 1960s, causing public outrage.
Roberts and two associates - John Duddy and John Witney - had been sitting in a van near Wormwood Scrubs prison when three policemen approached to ask questions.
Roberts shot dead Mr Wombwell and Mr Head, while Mr Fox was killed by another member of the gang.
The officers were killed in front of children playing in the street.
'Not a bad bone'
Roberts was on the run for 90 days, using his Army jungle training to camp out in Hertfordshire, where he was eventually arrested.
He has now been in prison for 18 years longer than the 30-year minimum term recommended by the trial judge.
But John Tully, chair of the Metropolitan Police Federation tweeted: "This man should never see the light of day again, life should mean life."
A former inmate called Mark, who spent some time in prison with Roberts, phoned BBC London 94.9 to say there "isn't a bad bone in his body".
He said: "It's terrible for the officers losing their life but the man's done 48 years. I don't think on the day they went out to murder people."
Mark said the murders had happened "in the heat of the moment".
Mayor of London Boris Johnson said Londoners would be "absolutely sickened by this news".
"They will find it hard to understand how a man who shot dead three police officers in this city in the most horrific fashion can now enjoy the freedom he denied his victims," he said.
"To my mind, in the case of the murder of a police officer, life should mean life."
A Ministry of Justice spokesperson said: "The release of life sentence prisoners is directed by the independent Parole Board once they are satisfied they can be safely managed in the community.
"Once released they are subject to strict controls for as long as their risk requires them. If they fail to comply with these conditions they can be immediately returned to prison."
Roberts' accomplices John Witney and John Duddy were both handed the same sentence as Roberts.
John Witney was released on life licence in 1991 after serving nearly 25 years but was found murdered in Bristol eight years later. John Duddy has also died.
In May, Justice Secretary Chris Grayling announced plans to change the law so that the killers of police or prison officers would face whole-life prison terms.
"It is essential that police and prison officers feel the full weight of the state is behind them as they fulfil their crucial duties," he said.