A Metropolitan Police officer who was shot dead at a south London custody suite was a “long-serving sergeant”, Met Commissioner Cressida Dick has said.

The victim died in hospital after the gunman, who was being detained for possession of ammunition and class B drugs, opened fire at Croydon custody centre in south London during the early hours of Friday.

The 23-year-old murder suspect, who is believed to have shot himself, is in a critical condition in hospital.

He was not regarded a subject of interest by security services, the PA news agency understands, but reports suggest he may have previously been referred to the anti-extremism Prevent programme.

The Independent Office for Police Conduct, which is investigating due to a member of the public being seriously injured in police custody, said the suspect was in handcuffs when shots were fired.

IOPC regional director Sal Naseem said: “What we have established is that the man was arrested for possession of class B drugs with intent to supply and possession of ammunition.

“The man was handcuffed to the rear before being transported to Croydon Custody Suite in a police vehicle where he was escorted into the building. He remained handcuffed to the rear and seated in a holding area in the custody suite.

“His handcuffs remained in place while officers prepared to search him using a metal detector.

“It is at the point that shots were fired resulting in the fatal injuries to the officer and critical injuries to the man. A non-police issue firearm, which appears to be a revolver, has been recovered from the scene. Further ballistic work will be required.”

A murder probe has been launched and investigators from the IOPC watchdog were at the scene to establish how the gun got into the custody suite.

Speaking from the scene, where floral tributes were left throughout the day, a friend who played rugby with the officer described him as “an inspiration” who was looking forward to retirement.

The 27-year-old, who gave his name as Paul, said: “The man was a machine. He went from training with us last night to come to his shift work here in Croydon. He would do that week in and week out.”

Dame Cressida led police officers across the capital in a minute’s silence at 4pm.

She said: “This morning we learnt of the shocking death of a much-loved colleague, a long-serving sergeant in the Metropolitan Police who was working last night in our Croydon custody suite.

“I have visited and spoken to our officer’s partner together with other colleagues. We are giving her the best support we can.”

She added: “Early indications are that the suspect shot himself. This has not yet been established as fact. The man remains in a critical condition in hospital.

“I understand that there is considerable interest in the identity of the officer but we have not yet been able to inform all of his close family.”

Leroy Logan, a former Met superintendent, said there were questions about the circumstances which led to the shooting.

“How did that person come to be in the station, whether it’s in the yard or the building itself, and be able to produce a weapon, whether it’s on them at the time?” he told BBC News.

“It depends on the calibre of the weapon, because obviously if it’s a small weapon and it can be easily in that person’s clothing, then obviously it brings another question on how thoroughly that person was searched, if at all.

“Those are the things the department for professional standards will look at and the IOPC as well as the investigating officers who will have to look at this thing thoroughly.”

The officer is thought to be the first to be killed in a shooting in the line of duty since Pcs Fiona Bone, 32, and Nicola Hughes, 23, in September 2012.

They were murdered by Dale Cregan in a gun and grenade attack while responding to a report of a burglary in Greater Manchester.

The Met sergeant is the 17th from the force to be killed by a firearm since the end of the Second World War, according to the National Police Memorial roll of honour.

Unarmed Pc Keith Palmer, stabbed in March 2017 by terrorist Khalid Masood during the Westminster Bridge attack, was the last Met officer to be killed in the line of duty.

Another hero has been taken from us in unwarranted violence

The roll of honour includes Pc Andrew Harper, who died when he was caught in a tow rope and dragged along country lanes after trying to stop quad bike thieves in Berkshire in August 2019.

The Thames Valley Police officer’s three teenage killers were cleared of murder but convicted of manslaughter after an Old Bailey trial.

His widow Lissie Harper, who is campaigning for a change to the law which would see all those convicted of killing emergency workers receive a life sentence, said: “This is devastating news.

“No person should go to work never to return. No human being should be stripped of their life in a barbaric act of crime.

“Another hero has been taken from us in unwarranted violence.”

Prime Minister Boris Johnson tweeted: “My deepest condolences go to the family, friends and colleagues of the police officer who was killed in Croydon last night.

“We owe a huge debt to those who risk their own lives to keep us safe.”

Home Secretary Priti Patel said: “I’m deeply shocked and saddened by the tragic killing of the officer in Croydon overnight.

“All our thoughts are with the officer’s family, friends and colleagues across the Metropolitan Police force, but also policing family across the country.

“This is a sad day for our country as once again we see the tragic killing of a police officer in the line of duty as they’re trying to protect us and keep us safe.”

Mayor of London Sadiq Khan said: “I am devastated by the news a Metropolitan Police officer has lost his life.

“I was informed of this tragic incident by the Commissioner this morning, and my heart goes out to the family of this brave officer, who has paid the ultimate price for helping to keep Londoners safe.”

Forensic officers in white suits were seen entering the police station on Friday.

Local resident Wilhemina Dew, 45, said: “It makes me feel scared.”

She added: “Whatever the reason, whatever the tensions shooting the police is unacceptable because we all need to feel safe.”

Reverend Catherine Tucker, of the Holy Church Croydon parish, 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.”

She added: “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.”