Drug workers estimate there are around 1,000 shops selling khat leaves, including murungi and the less potent hereri, in London. Tonnes of it arrive fresh at Heathrow every day. As Ali explained to me, there is no shortage of supply. I said I would consider his offer and we parted at Cafe Buz. In the street, a group of men lounged listlessly, their eyes bloodshot, telltale green flecks at the corner of their mouths. Here, and on the other side of the Atlantic, people like this are making Ali rich - certainly rich enough to tempt young women into risking their liberty to undertake a "trip of a lifetime".