As many as 800 young people crowded a central city street during the London Marathon, drinking alcohol and inhaling nitrous oxide, according to a new police report.
A pram was tipped over amid the melee, details of which have emerged as authorities plot how to prevent a repeat of the incident.
The new report reveals police recorded antisocial behaviour by up to 800 youths in the Byward Street area on April 22 during the marathon, adjacent to the Tower of London leg of the route.
The report on the incident was provided to the City of London Corporation public safety committee on Thursday (May 31).
City of London Police's Superintendent Lee Presland told the committee he ran this year's marathon and had noticed a change in the atmosphere.
He said: “You actually picked up a different vibe at that point, some quite nasty comments, which is not perfect."
The crowds had no interest in the actual marathon, he said.
The report said the incident resulted in four arrests for assault, and extra officers had to be sent to the area to disperse the crowd.
Officers were able to use a power to direct people to leave a public area and not return for up to 48 hours, but it proved difficult to enforce.
City businesss representative Bob Benton said he had noticed the state of the area around Fenchurch Street station following the marathon.
“It looked like a riot had come through," he said.
He had seen small silver containers littered around outside the station the day after the event.
“What that’s got to do with people running from the marathon I'm not quite sure,” he said.
“Perhaps someone had twisted their ankle,” responded the City's London Fire Brigade borough commander John Simpson.
The contents of the small silver bullet-shaped nitrous oxide containers are meant for use as whipped cream chargers, and emit the same kind of laughing gas dentists use as a sedative.
When used recreationally, they are known as "NOS" or "nangs," and the gas is usually taken in using balloons for a fleeting high.
The report came out amid a focus on youth crime in the capital, where police are dealing with a rise in knife crime and homicides.
The report also noted multiple City authorities were working with police to manage a "steep" increase in young people cycling in large numbers at the weekends, around Castle Baynard Street and Tower Place, a short walk away from the marathon incident.
Reports to police mentioned the young people being aggressive, throwing bottles and being intimidating, and in one case assaulting a pizza delivery driver.
The report suggested a public space protection order being put in place ahead of the marathon would have made it easier for police to enforce order.
The City's community safety team plans to work with police and Tower Hamlets authorities to take steps to avoid a recurrence at the next event.
