A police officer has been shot dead at Croydon Custody Centre in south London.
The male officer was shot when a man, who was being detained, produced a weapon during a search. The suspect then turned the gun on himself.
The officer was treated at the scene overnight but died in hospital. A 23-year-old man is in a critical condition after being treated for gunshot wounds.
Prime Minister Boris Johnson said “We owe a huge debt to those who risk their own lives to keep us safe.”
In a post on social media he also said: “My deepest condolences go to the family, friends and colleagues of the police officer who was killed in Croydon last night.”
No police firearms were discharged during the incident at about 02:15 BST at the Windmill Road centre, the Met Police said. The officer’s family are being supported by specialist officers.
Asked about how someone could enter the building while armed, former Det Ch Insp Chris Phillips said: “When people get arrested there is a general view that they should be searched before being transported to the police station but that doesn’t always happen – and it depends on what the man was arrested for in the first place.
“This goes down the line about handcuffing – do you handcuff, when do the handcuffs get taken off for protection etc.”
Reverend Catherine Tucker, who was at the centre earlier, said: “The action taken against the police is really unacceptable but I also feel sorry for the perpetrator.
“Sadly, I am not surprised there has been a shooting in Croydon.
“There are tensions between the police and young people particularly in relation to stop and search and the way the police relate to the community.”
Met Commissioner Cressida Dick described the loss of her colleague as “truly shocking”.
“We are currently supporting his family and also have a dedicated team providing support to the officers and those in the custody centre who witnessed the shooting,” she said.
“When a colleague dies in the line of duty the shockwaves and sadness reverberates throughout the Met and our communities. Policing is a family, within London and nationally, and we will all deeply mourn our colleague.”
By Dominic Casciani, BBC Home Affairs correspondent
This appalling incident in Croydon appears to be absolutely unique – and the shock felt today underlines how rare it is for police officers in the UK to lose their life in the line of duty.
The Metropolitan Police officer shot dead in Croydon is the 17th from the force to have been killed by a firearm since the Second World War.
But since the beginning of the 20th Century, only 73 police officers have been shot and killed by criminals in the UK, excluding all deaths in Northern Ireland.
The majority of those deaths – more than 50 – have occurred since 1945.
Police officers in other parts of the world are often puzzled why British constables are not routinely armed. But the fact is that there are very few criminal guns in circulation – and the culture of policing has never seen it as acceptable to be universally armed.
However, Tasers are increasingly a common sight in the UK – and a massive survey of police officers recently found three-quarters would carry one of the less-than-lethal devices on the frontline, if given the choice.
Home Secretary Priti Patel said: “I am deeply shocked and saddened to learn that a Metropolitan Police Officer has been shot and killed in the line of duty.
“This is a sad day for our country and another terrible reminder of how our police officers put themselves in danger each and every day to keep the rest of us safe.”
‘Sick to their stomachs’
Ken Marsh, chairman of the Met Police Federation, said: “The murder of a colleague on duty is utterly devastating news.
“Officers across London are in shock and sick to their stomachs at the nature of his death.
“Sadly, on very rare occasions officers make the ultimate sacrifice whilst fulfilling their role. When that happens we will ensure their bravery and sacrifice is never forgotten.”
The incident has been referred to the Independent Office for Police Conduct which will lead an independent investigation.
The Met continues to investigate the officer’s murder.