Knife arches are being installed at Notting Hill Carnival for the first time after a wave of violent crime in the capital.
The metal detection systems will be placed at “strategic points” along the route of the west London street party, though the Metropolitan Police did not disclose where.
It is hoped the “tried and tested” method will put off those planning to arm themselves with knives and offensive weapons but not everybody will be expected to pass through them, according to the Met.
The news comes after threats of acid attacks were reportedly circulating on social media.
According to The Sun, Snapchat posts have been warning people will be “splashed with acid”. The veracity of the posts is not known, but have been enough to put some people off attending the event.
One person who posted screenhots of the threats on Twitter said: “This shit isn’t even funny!!! I’m happily staying at home, ppl are honestly too immature.”
There were more than 40,000 knife-related incidents in London in the year up to March 2018.
The bank holiday weekend event will also be policed by the highest number of officers in six years.
Superintendent Elisabeth Chapple, Met spokeswoman on the carnival, said: “We want people to come to the carnival to enjoy themselves, and therefore we want to reassure people there is a significant policing plan in place working in support of the organisers to help them do that.
“We have a significant policing plan in place and have been doing a lot of activity that would deter anybody who might want to cause trouble at carnival from coming.”
Using the knife arches is part of a wide-ranging “belt and braces” approach to try to make the event safe, according to Notting Hill Carnival Limited executive director Matthew Phillip.
He said: “London as a whole and the UK is operating under a backdrop of knife crime, and we are working to have a safe carnival. The introduction of the knife arches is one thing we have as we to try to do that.
“Most people who come to carnival come to enjoy themselves, and we want that spirit of safety and unity.”
Some 13,000 officers will be deployed to the two-day event – around 450 more than last year and more than the parades over the past five years.
Nearly 7,000 officers, some from the Metropolitan Police’s newly formed Violent Crime Task Force, will be policing Monday’s event to “combat the threat of violent crime”.
This will be up from 6,100 on-duty officers on Sunday’s less busy family day.
Undercover police officers, as well as officers from the force firearms and dog units, will be in place.
The event is expected to attract more than one million revellers to its floats, food stalls and music.
The music is set to stop for a 72-second silence in tribute to the 72 people who died following the fire at Grenfell Tower in June 2017.
The tower block is within half a mile of the parade route.
Partygoers are advised to plan their journeys ahead, avoid bringing valuables and not carry too much cash.
Supt Chapple added: “There are no specific threats to carnival this year but we continue to review the policing plan in relation to it.
“We are aware that in previous years there have been a number of incidents but compared with the number of people coming to carnival the number of incidents isn’t significant, but any incident that does affect Londoners we want to provide reassurance.”
Commander Dave Musker, police gold commander for the event, said: “The Met seeks to support Notting Hill Carnival Ltd, carnivalists and local communities to deliver a safe and spectacular event over the bank holiday weekend.
“Our continued major effort directed against violence across the capital will continue.”
He added: “Let no-one be in any doubt that if you have the intention to come to carnival and be involved in crime or violence, my officers will robustly and proactively target you to keep Londoners safe.”