Britain already has Europe’s highest proportion of heroin addicts, and last year, drug-related deaths hit a record high in England and Wales, with 3,744 deaths mainly from heroin and other opioids. While the scale is small compared with deaths in the United States — where more than 100 Americans die each day from opioid abuse — British authorities fear that fentanyl could become the country’s next most dangerous drug.

“People here are prescribed opioids for pain, but nothing to the extent of the U.S., where extremely potent opioids are being prescribed on a large scale,” said Dr. Prun Bijral, the medical director for Change, Grow, Live, a nonprofit organization that focuses on substance abuse. “On the one hand, this is positive. But on the other hand, the U.K. has one of the highest rates of drug-related deaths in Europe.”

No place has been hit harder by heroin, fentanyl and opioid addiction recently than Hull, a former fishing town of 260,000 people about 150 miles north of London that was improbably named Britain’s 2017 “City of Culture.” On a drizzly cold day last month, under a bright green sign welcoming visitors to the city, several addicts lay bundled up, stashes of drugs and alcohol secreted in blankets and other belongings. Others lined the doorways of nondescript buildings on the city’s main street.

Since the fishing industry collapsed in the 1970s, the city has suffered some of the highest rates of unemployment — currently 8.9 percent — and addiction in the country. The city’s easy transport links to the port and two major highways also facilitate drug trafficking.