A teenager addicted to cannabis slashed an autistic man across the face with a kitchen knife in a terrifying robbery carried out to feed his habit.

Mario Howe-Cossali, 18, stalked his victim through Canterbury city centre and stole his mobile phone after slicing his lip and ear with the seven-inch blade.

But the violence did not stop there, as minutes later the attacker found his victim on a high street payphone reporting the robbery to police.

He pulled the man out of the kiosk, pushed a bottle to his back and then "frogmarched" him to a bin store behind the ABode Hotel.

CCTV played at Canterbury Crown Court showed Howe-Cosalli then smash a bottle over the man's head, screaming: “You don’t know who you’re messing with.”

He could then be seen throwing various other bottles at his victim, who had fallen to the floor with cuts to his head, and fractures to both hands.

When Howe-Cossali fled, the man sought refuge in McDonald’s and emergency crews were alerted.

The victim was taken to hospital, where glass was removed from his head, cuts were sealed and fractures treated.

Meanwhile, Canterbury Cathedral officers discovered the injured man's Sony Xperia smashed in the Buttermarket.

Howe-Cossali - still armed with the knife - was found nearby with blood on his shoe.

He told officers the blood was from beating someone up who offended his girlfriend.

The victim told the court that since the attack he no longer takes early-morning walks, which he had preferred because fewer people were out.

Howe-Cossali was 17 at the time of the offence in February last year and had no previous convictions.

He had recently been diagnosed with autism and attention deficit hyperactivity disorder, and had developed a cannabis problem.

The court heard Howe-Cossali was trying to rob strangers to fund his addiction.

His barrister, James Howard, and psychiatrists argued he would benefit from the intervention of a hospital order rather than custody.

But Judge Mark Weekes sentenced Howe-Cossali to two years and seven months in a Young Offenders' Institute for the "gratuitous violence".

The judge said he was "not persuaded there is sufficient nexus that is attributable to those conditions".

"In my judgement your behaviour demonstrated a number of deliberate acts on your part," he said.

He argued that were Howe-Cosalli to be sentenced to a hospital order, any defendant with similar learning difficulties could be granted the same.

Howe-Cossali, of Ramsgate Road in Margate, pleaded guilty to wounding with intent, robbery, carrying a blade and damaging property.

Read more: All the latest news from Canterbury