A Somali man who was stabbed to death in Streatham last night was chewing khat with a group of about 10 men just before he was attacked, a witness has said.

The man was attacked at the rear of Waaberi Business Centre in Gleneldon Mews at about 7.15pm.

Khat, a stimulant chewed in east Africa, is popular in the Somali community, but some members hold it responsible for social breakdown.

It is legal in Britain, but banned across America, Canada and most of Europe.

One witness said he heard screaming while working in his garage and came out to find the man bleeding at the neck.

He said before the murder he saw a group of about 10 young men sitting together eating khat on a terrace at the back of the shop.

He said: “I could see the tension. I knew something was going to go down.”

Police said the man was 24 years old, but at the crime scene today his sister said her dead brother was 20 and had a daughter.

She did not want to talk but simply said: “I lost my brother”.

Despite efforts of an ambulance crew and medical team in a car, the man was pronounced dead behind the property, the front of which is in Streatham High Road, at 8.20pm.

The scene remained cordoned off by police this morning.

Detective Chief Inspector Charles King, who is leading the murder investigation, said: "At this early stage we do not believe this man had any gang links and we retain an open mind regarding the motive for this attack.

"Clearly, he was the victim of a brutal assault and I would urge anyone with any information that may assist my officers to come forward.

“I can assure you that you will be treated with the utmost discretion."

A post mortem examination will take place at Greenwich mortuary. No arrests have been made.

Anybody with information should call police on 020 8721 4054 or Crimestoppers anonymously on 0800 555 111.

Contact the reporter on alice.foster@london.newsquest.co.uk or 0208 722 6337.