More than a million people are expected to descend on the Notting Hill carnival this weekend but watching overhead will be a team of police "super recognisers" who have been selected for their ability to spot known offenders among the crowds.
But as the two days of celebrations get under way along the carnival route, 17 specialist officers will be holed up in a central control room several miles away in Earls Court monitoring live footage in an attempt to identify known offenders.
Chief superintendent Mick Johnson from the Metropolitan police said it was the first time the "recognisers" who have been selected for their ability to remember hundreds of offenders' faces have been used to monitor a live event.
"This type of proactive operation is the first one we have done in earnest in real time so we are going to be looking at it very closely to see how effective it is and what we get out of it," he said.
The Met has 180 so-called super recognisers most of whom came to the fore in the aftermath of the London riots when they managed to identify more than a quarter of the suspects who were caught on CCTV footage.
The officers will have access to 80 cameras that can zoom in to track suspects as well as roving police camera teams. The aim is to spot known offenders or potential flashpoints and direct officers on the ground to prevent crimes being committed.
One of the super recognisers on duty will be Patrick O'Riordan, who says he has had an ability to pick people out in a crowd and recall faces since he joined the Met 11 years ago.
"It is with me all the time. Often when I am on a day off or out with my girlfriend I will see someone and know straight away who they are and where they fit in," said 45-year-old. "It could be their eyes or the shape of their forehead or their gait, but something usually sticks with me. It something that started from day one as a police officer really it is just something that I took too naturally."
Meanwhile, as the final preparations are put in place for the carnival, concerns have been raised about emergency fire cover at the weekend after London Fire Brigade withdrew 27 fire engines including one of two based at Ladbroke Grove on the carnival route in preparation for a potential strike by crews over pension provision.
Labour London Assembly fire spokesperson Fiona Twycross said it was a "very worrying" move. "I have written to the London fire commissioner asking for an urgent explanation as to what contingency arrangements are in place for the carnival, what the response time will be for the nearest units and what risk analysis was carried out before this fire engine was removed," she said.
London Fire Brigade confirmed it had removed the fire engines to ensure it could provide cover if firefighters vote to strike. But London fire commissioner Ron Dobson denied it would have any impact on safety. "Despite having temporarily withdrawn 27 fire engines to prepare for a potential firefighter strike, fire cover across the rest of London will not be affected and our target times of getting a fire engine to the scene of an incident within six minutes, and a second within eight, won't be affected."
This year's carnival is the 49th in the event's history and is expected to draw more than a million people over two days. The carnival route will be lined with music systems and hundreds of floats and bands will form the main attraction.
Earlier this week police arrested 112 people in raids targeting would-be suspects ahead of this weekend's carnival.
The operation, carried out by a 250-strong team of officers across London, targeted gang crime, drug supply and other offences that could have an impact on the safety of carnival. A handgun, two imitation firearms, '4,000 in cash and a Porsche were seized.
Johnson said: "We are intent on ensuring that those who plan on coming to the carnival to commit crime of any kind are prevented from doing so, which is why we will be using a team of super recognisers. This will enable us to quickly identify offenders on the day and ensure that if they are not caught at the event, we will be able to track them down and arrest them afterwards."
Two years ago the future of the event appeared to be under threat following disagreements about the level of policing and internal disputes that saw two of its co-directors quit.
But Vincent John, director of the London Notting Hill Carnival Enterprises Trust said the event had turned the corner and was now on a stronger footing.
"We had a very successful year last year and we are expecting a similar event this year."
He said organisers had worked hard to represent all the different interest groups, from the people that run the sound systems and bands to the local residents, and had put a lot of work into improving the artistic quality on show.
"We have tried to sharpen things up and to improve the quality of what we do at the same time as remembering that in the end this is a street carnival depicting African-Caribbean culture as it integrates with the UK."