Some of the most vocal critics of the drug have emerged recently from within the Somali community here. Khat, they say, is not only bringing harm to individuals, but it's also stymieing wider integration efforts.
"My people are in trouble because of this drug and I tell you ... London hasn't seen the worst of it," says Abdi Hussein, a young Somali migrant and former addict.
Thus far, Britain's Home Office has parried arguments for controlling khat, saying it is a mild narcotic and an innocent cultural past time with few proven social or medical ills.
'Khat has slowly been killing our community'
Each week, according to a widely cited but likely outdated government estimate, around seven tons of the leafy stimulant arrives at Heathrow Airport from the khat fields of Ethiopia and Kenya, to be whisked to khat cafes, known as mafreshis, frequented by many of Britain's 250,000-strong Somali migrant community, as well as the country's smaller Ethiopian and Yemeni groups.
Chewers devour up to two pounds of the leaf in a session. Similar to the chewing of cocoa leaves among Andean people, khat use is a centuries-old tradition originating in East Africa and the Arabian peninsula.