A teenager stabbed a man to death on Oxford Street during an argument to settle the score and assuage his wounded pride, a court heard.

Anthony Costa, 19, from Gainsford Road Walthamstow, is accused of murder, after killing the 20-year-old by a single stab wound to the heart in the middle of the afternoon, but claims he was acting in self-defence during the fight between two groups of youths on May 12.

The Old Bailey heard he was arrested after his mother, Gillian Costa went to the police “with considerable courage and fortitude” after she confronted him and he admitted the stabbing.

He told her he stabbed the man after being confronted by 15 boys but that he had got up and walked away afterwards.

The victim, who cannot be named for legal reasons, was one of a group of youths Costa argued with outside McDonalds in London's busiest shopping street, in full view of witnesses and CCTV.

Jacob Hallam, prosecuting, said there was aggression from both sides, shouting, jostling and pushing. Costa and his friends walked away but a drink was thrown at their backs.

He said the jury would hear from witnesses who overheard the three egging each other on and others who saw them puffing up their chests and pulling their shoulders back.

Mr Hallam added: “He turned round and went back. Anthony Costa pulled the knife that he had taken on the shopping trip from out of his trousers, armed himself with it and he returned to the argument that he had walked away from he used the knife to stab that man.

“He could've run away, he could've turned round and argued. He could've if he wanted fought and used his fists. He didn't. Instead he chose to use his knife, a knife he wasn't supposed to be carrying.”

Another witness described seeing what looked like somebody pushing the man who then fell to the floor and then began to bleed heavily, Mr Hallam said.

The three split up and ran, Costa ran he bumped into several shoppers and dropped the knife.

Despite several people coming to his aid, including two nearby doctors, the victim died in the street A post mortem found he had died from a catastrophic blood loss to the heart.

The trial continues.