Four teenagers held as Ben's sisters lead march

The arrests came as more than 300 people marched through north London today in memory of the murdered GCSE student.

Three teenagers were held by detectives late yesterday while a fourth handed himself in to police in east London this morning, in a development described as "significant" by a senior detective.

The brother of former EastEnders actress Brooke Kinsella was knifed to death when he was caught up in a fight that spilled out of an end-of-term party at an Islington bar early on Sunday. He was stabbed four times in the neck and chest after being chased by four black youths during the fight.

Police said today one person was arrested in Islington yesterday afternoon, and two more were held at an address in Chadwell Heath late last night. All were aged 18. The fourth, a 19-year-old, handed himself in at Bethnal Green police station this morning.

All those held lived in Islington and were being questioned today.

At this afternoon's march, friends, neighbours, teachers and others walked from Islington Town Hall to York Way where Ben was stabbed to death to lay flowers. Brooke Kinsella joined the march wearing a T-shirt with a photograph of Ben as a baby.

The group stopped and stood in silence outside Shillibeers, the bar where Ben had been on the night he died. As they approached the spot, the crowd began shouting: "What are we here for? Ben. Why are we here? No knives."

Miss Kinsella, 24, who played Kelly Taylor in the BBC soap, said: "I haven't the strength or the energy to say everything I want. I want to say thank you to every single person who is here and everyone else thinking of him."

She added: "Please, please, if anybody knows anything please can you help and get in touch with the police."

Gracie Carter, 16, said: "Ben was the sweetest boy you could ever meet. If someone like Ben could get stabbed then it could happen to anyone. It needs to stop now." Max Tshoukas, 16, said: "I used to play football with Ben. He was never the type to go looking for trouble."

Organiser Brooke Dunford, 16, had printed leaflets, sent emails, texts, and used internet site Facebook to ensure so many people turned up.

A close friend of Ben since she was 12, she said: "I couldn't just sit around and grieve when this might happen to other people."

She was wearing a T-shirt bearing the slogan "18?" - a reference to whether she could be the 18th teenager to be knifed to death in London this year.

Miss Dunford said she had called the event "Life For Life" because she believed a life sentence should be mandatory for anyone found guilty of killing a person.

Ben died in the arms of his friend Louis Robson, 16, the son of Birds Of A Feather actress Linda Robson.

Ms Robson, speaking on GMTV, said today: "If [children] are found with a knife, they have got to be sent away, there's no court cases, there is no out on bail."

The arrests came after it emerged that Ben foretold his own violent death in a school essay he wrote weeks before he died. In it he describes staring up at his killer, and told how he had fallen victim to "the monstrosity society had become" after being repeatedly stabbed in the chest, back and stomach.

It also emerged Ben had been repeatedly threatened at the internet café where he worked after he stopped youths stealing a mountain bike from outside.

Jonathan Laidlaw, his boss at Zebedee, in Islington, said: "They were saying, 'Where is he? We're going to stab him'."

Detective Chief Inspector John Macdonald said: "There were 150 people in the pub that night. I urge them to come forward."

Officers recovered two knives in the area yesterday and tests were being carried out to establish if either was the murder weapon.