opium

"When I first started work, you could buy poppy heads - opium," she said.

Unlike synthetic opioids produced using chemicals in a lab, heroin and morphine are refined from the gum extracted from Papaver somniferum, the opium poppy.

He said their introduction into the UK market appears to have followed a steep reduction in the production of heroin, after the government in Afghanistan cracked down on the production of opium poppies.

In April, the Thai authorities quietly eased restrictions on opium and psilocybin "magic" mushrooms, allowing them to be used for medicine and research, signalling yet more potential drug reform.

Its mission: destroy opium poppies used to make heroin.