A form of high-grade white heroin is making a comeback on Britain's streets, the Serious Organised Crime Agency (Soca) has warned.
Heroin hydrochloride was widespread during the 1970s but was replaced by more well-known "brown" heroin.
Easy to snort and inject because it is water-soluble, white heroin's dangers were made clear in Quentin Tarantino's cult film Pulp Fiction, in which Uma Thurman's character snorts the powder, thinking it is cocaine, and then collapses.
Soca has warned of a resurgence in the drug in the UK, manufactured and shipped in from Afghanistan.
Deputy director Steve Coates said there had been a few seizures of small amounts of white heroin in the past year but the return of the drug was noticeable.
He said there had been seizures overseas in Afghanistan and Turkey, as well as a huge haul last year of £5.5 million worth of heroin, including white heroin, in straws sewn into the weave of Afghan rugs.
Mr Coates, who has been involved in investigating the heroin trade for more than 20 years, said law enforcement agencies had seen a "seismic change" in the supply to the UK.
Overseas seizures in Afghanistan and Turkey suggest large-scale producers have started to manufacture white heroin and export it to the UK.
Mr Coates said Soca is working with partners in the UK and Afghanistan and Turkey to stop the lethal drug reaching the UK.
Soca's aim is to warn police, drugs charities and users of the return of white heroin and its dangers, he said.
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