There has never been a more dangerous time to be taking drugs, the head of the National Crime Agency (NCA) has warned.

Director-general Graeme Biggar said drugs were the biggest single driver of organised crime in the UK and remained the “most important crime type” for the law enforcement agency to be tackling as he raised concerns about a “significant” number of deaths linked to the “incredibly strong” synthetic opioid nitazene in the last year.

Outlining the NCA’s annual assessment of crime threats to Britain, he said: “There has never been a more dangerous time to be taking drugs.

“The number of people that have died from the misuse of drugs has increased by 60% over the last 10 years and tripled over the last 30 years.

“That gives us one of the highest death rates for drugs in Europe.”

At the briefing in central London on Thursday, he told reporters that over the last year the NCA had seen the presence of synthetic opioids in greater numbers after previously emerging in small levels in the form of drugs such as fentanyl.

Since the “surge” in nitazene began in June last year – which is being used as a cheap way to increase the strength of certain drugs – there have been 284 confirmed deaths from nitazene or versions of it to date, he said, but stressed the number is likely to rise as investigations into other deaths continue.

“That is a relatively small proportion of overall drug deaths, but it has been growing. It is significant,” Mr Biggar said, adding: “From nitazene, you can absolutely die the very first time you take it, and from nitazene, you very often don’t know you are taking it.

“It is heroin that’s been adulterated. It’s been put into a pill that you think is something else. And so anyone, a teenager, might be taking a drug thinking it is something else, and it’s nitazene. It is incredibly strong, and you die.”

In the majority of nitazene cases, the substance was “consumed unintentionally alongside other drugs such as heroin and/or benzodiazepines, with very small quantities capable of leading to overdose and death”, a document setting out the NCA’s national strategic assessment said, adding: “We must prepare for these substances to become widely available, both unadvertised in fortified mixes, and in response to user demand as a more potent high.”

Mr Biggar said his warnings applied to anyone who takes recreational drugs as he highlighted that the NCA estimated the cost to society in the UK from the misuse of drugs is £20 billion.

NCA bosses also told how drug mules were “brazenly” flying into the UK with suitcases stuffed full of cannabis without even trying to hide it.

Mr Biggar said cannabis remains the “biggest single drug consumed in the UK” as he described how the NCA had noticed a “significant increase” in the last two years of airline passengers trying to bring the drug into the country in their luggage.

Turning to child sexual abuse, Rob Jones, the NCA’s director general of operations, said it is “still continuing to demand a big resource-intensive effort” to tackle.

The NCA threat assessment estimated there are between 710,000 and 840,000 UK-based adult offenders who pose varying degrees of risk to children, equivalent to 1.3% to 1.6% of the UK adult population.

“That is the threat to children in the UK from people who may have a sexual interest in them,” Mr Jones said, adding: “Those figures are eye-watering, but they’ve been out there for many years now, and they stack up”.

He drew attention to “high profile individuals, people of public prominence, being arrested and dealt with for this crime. And we can continue to see children being harmed online as a result of it”.

His comments come in the wake of disgraced veteran BBC News presenter Huw Edwards pleading guilty to charges of making indecent images of children, with the court hearing he had been involved in an online chat with a man on WhatsApp between 2020 and 2021 who sent him hundreds of sexual images, of which 41 were indecent images of children.

The NCA has seen changes in the threat to children with the “significance of sextortion”, Mr Jones also warned as he told how “sextortion groups doubled down with a new playbook in terms of trying to inflict misery on children through extortion tactics” to make money.

He said it is important to have “open conversations” with children about the tactic of coercion to extort sexual favours from a victim because it will “completely change the power dynamic”.

He added: “If children feel they can reach out and say, I’ve shared a compromising picture, I’ve shared a compromising chat, the people who are trying to extort them have no power over them whatsoever.”

The NCA repeated concerns that dangerous migrant Channel crossings were a “persistent and high-volume threat” in the wake of more deaths at sea, with Mr Biggar suggesting an asylum system that works “quickly and effectively” could help deter the numbers of people attempting the journey.