Britain’s top police officer Cressida Dick said the vast majority of Londoners support increased police stop-and-search powers to combat “outrageous” levels of knife crime in the capital.

Met police commissioner Ms Dick reaffirmed her commitment to driving down the epidemic - which has seen 14 murders from knife-related attacks in the past four weeks - after coming face-to-face with families in Wandsworth, a borough where three people have been stabbed to death this month.

It came as the latest victim, a 20-year-old man, was stabbed to death in front of his horrified girlfriend, according to witnesses, as the couple walked back to their car from a cinema in Romford.

Witnesses said the young man was ambushed and chased by a gang of youths following a matinee screening at the Brewery Shopping Centre.

Speaking at the Ashburton Youth Centre in Putney, the commissioner said: “I’ve been talking a lot about stop and search in the past five weeks and very few people say they don’t want them or are concerned about them.

“It appals me to think young people are losing their lives in this way, it’s outrageous. However you measure it there is too much of it.

“If police carrying stop and search can help to stop that then the vast majority of people will be very supportive.”

She promised more officers in schools in every area of London to help build relationships with young people after being told children as young as six were carrying blades on some housing estates, because they “feel naked” without them.

The commissioner said: “It’s outrageous to hear a six-year-old is carrying a knife, for whatever reason.

“It’s extraordinarily young. It’s important that our message on the danger of knives gets through to them at an early age, including in primary schools.”

Ms Dick said youngsters often carry knives for “some kind of respect, some kind of kudos”, but added: “I do accept there are places where some of our young people are scared and they feel it makes sense to carry a knife.

“I can say as long as I live that it does not make them safer. They may not hear that message from me - we need to get people in communities, people in schools, parents understanding and helping young people to understand that it will end in tragedy, probably, for them.”

Ms Dick also held a private meeting with the family of Lewis Elwin, a 20-year-old trainee electrician who was stabbed to death last year next to Sadiq Khan’s Tooting home.

His mother Sharon, urged witnesses to come forward and catch the killer of her son, saying: “We hope this is the start of solving the problem because no mother should go through this, people are fed up - we’ve had enough.”

The latest killing took place at around 4.30pm yesterday.

Desperate passers-by administered first aid before the man was rushed to hospital.

But doctors could not save him and he was pronounced dead an hour later.

Jodie Freeman, 22, who gave the victim CPR, said: “He had been stabbed on his left side, either in the heart or close to it.

“He was trying to speak but he didn’t manage to say anything. He was struggling to breathe.”

She added: “I’m emotionally in shock, I feel guilty about it because I couldn’t do more.

“Washing his blood off my hands has got to be the worst moment of my life. I’m so sorry I couldn’t save him.”

Four men were today being questioned on suspicion of murder at separate east London police stations.

The killing happened yards from where Joshua Acheampong, 19, was repeatedly stabbed outside Nandos restaurant in May 2014.