Britain’s biggest police force has seen its highest monthly number of violent deaths so far this year.

The Metropolitan Police has recorded 15 homicides so far in July, while figures on the force’s crime data website show there were nine in June and eight in May.

In March and April the figure was slightly above average, with 12 homicides recorded in each month, up from seven in February and 11 in January. This makes a total of 74 so far.

The latest death was a man aged in his 50s who was attacked in an amusement arcade in Camden High Street on Tuesday.

Customers fled the shop as violence broke out shortly after 10pm, and a member of staff locked the suspected attacker inside the building until police arrived.

Witness Joshua Lyons, 19, told the Evening Standard: “Everyone was hysterical and quite shaken up. About 10 customers were inside when it happened. The owner locked the doors. But that seemed to agitate him more and he carried on the attack.

“I saw a man being placed in handcuffs and put in the back of a police vehicle. Then the casino door opened and you could see the victim on the floor.

“He was motionless and they took his top off. They tried to do CPR and were pumping his chest. But people were repeating: ‘He’s dead.'”

Police are working to establish his identity and contact his family.

Anyone with information can call police on 101 giving the reference 7949/28jul, or to contact Crimestoppers anonymously on 0800 555111 or online.