It's a Wednesday evening in the City of London, and a strange crowd is gathering in the offices of DLA Piper, a global corporate law firm. Listen closely and you can hear the creak of expensive shoe leather as delegates reach for the tiny canapes and excellent wine. There are stockbrokers, hedge-fund managers and pension-fund investors, but also Essex farmers and quick-witted East End boys and girls here — all with an eye on the future of the nascent British medicinal cannabis industry.