Matt Ratana, 54, who was originally from New Zealand, died after he was shot at by Louis De Zoysa in a custody block in Croydon on September 25, 2020.

Sentencing De Zoysa at Northampton Crown Court, Mr Justice Jeremy Johnson told the 26-year-old: “You acted in cold blood. You intended to kill Sergeant Ratana.

“You aimed the gun at his chest at near point-blank range. Even as he fell you re-aimed and fired a second shot at him.

“The aggravating factors outweigh the mitigating factors. There is therefore no justification to depart from the starting point of a whole life order.”

De Zoysa, who is expected to be held at HMP Belmarsh in south-east London, showed no obvious reaction as he was told he will spend the rest of his life in prison.

He claimed diminished responsibility but was found guilty after a jury decided he pulled the antique weapon’s trigger deliberately to fire homemade bullets, and had not suffered an autistic meltdown.

Read more: Handcuffed man, 25, guilty of murdering Met Police sergeant Matt Ratana with revolver in London police station

Read more: Horrifying CCTV shows moment police officer Matt Ratana shot in custody cell by handcuffed man hiding gun behind back

The jury was previously shown CCTV footage of the moment when Sgt Ratana was fatally shot.

It showed De Zoysa seated on the custody bench, with his hands handcuffed behind his back, as Sgt Ratana entered the room and introduced himself.

He told the defendant: “You’ve been arrested on suspicion of possession of bullets, ammunition and possession with intent to supply class B.”

He went on to say: “Your detention’s not been authorised yet, but I can authorise a search of you under Section 54 of PACE.”

The defendant was then instructed to stand up for the search, at which point De Zoysa got up from his seat before uncovering a concealed gun from behind his jacket and shooting Matt Ratana.

Two separate police officers were stood either side of the defendant before tackling him to the ground as they shouted at him to surrender the gun.

De Zoysa continued to conceal the gun and fired it three more times before dropping it.

The second shot was fired during the police’s struggle with the defendant, which hit Sergeant Ratana in the leg – but this was not believed to be the fatal shot.

A third shot was fired in the direction of the wall, and finally a muffled fourth shot, which hit De Zoysa himself.

He was then tasered by a police officer and the gun was kicked away from the defendant and recovered by the officers.