Bitcoin Mining Operation Is Uncovered During U.K. Drug Bust

Unusual amounts of wiring and ventilation were visible on the outside of the building and a drone had measured high levels of heat rising from it—classic signs of a cannabis factory. But the officers broke in to discover a huge bank of computers in what they now suspect was a cryptocurrency mine.

They also found that the computers used stolen electricity by tapping directly into the power supply outside of the warehouse’s circuits. Police said the mine consumed thousands of pounds worth of electricity (£1 is equivalent to around $1.40).

Cryptocurrency mining, particularly for

bitcoin,

has become a lucrative business as its value has shot higher, peaking at about $60,000 per bitcoin in April. But mining the coins, where computers race to solve complex mathematical puzzles, is also hugely energy-intensive and very costly.

“My understanding is that mining for cryptocurrency is not itself illegal, but clearly abstracting electricity from the mains supply to power it is,” Sgt. Jennifer Griffin said in a statement on Thursday. She added that no arrests were made at the premises, but that the police would be making inquiries with the owner of the warehouse.

The British warehouse had “all the hallmarks of a cannabis cultivation setup,” Sgt. Griffin said. “It’s certainly not what we were expecting.”

Cryptocurrency mining has boomed as the value of bitcoins rocketed this year. When computers compete to harvest fresh coins by solving mathematical puzzles—a process known as mining—the new coins produced have fetched high prices.

On top of this, when a computer successfully solves the puzzle, it is able to process some bitcoin transactions on the network and can charge a fee for those services. Daily revenue from mining globally reached a record high of $77.8 million on April 15, according to CoinDesk, a research website that tracks cryptocurrencies. On that same day, bitcoin’s dollar value peaked at $63,381.20.

The process to obtain bitcoin is highly energy-intensive. As more people compete to harvest the cryptocurrency, the harder the mathematical puzzles get and the more energy is required to gain it. Bitcoin’s high energy use has drawn criticism in recent weeks from

Tesla Inc.’s

Elon Musk.

Chinese officials have also recently indicated that they will be taking measures to curb bitcoin mining in China, one of the largest markets for it. Some mining services have already started banning mainland China internet addresses from accessing their platforms in the wake of those comments.

Iran this week banned crypto mining for four months after a series of unplanned blackouts in cities. President

Hassan Rouhani

told a cabinet meeting that crypto mining was draining 2 gigawatts of electricity from Iran’s power grid each day, according to the BBC.

The fictional DeLorean time machine in “Back to the Future” needed just 1.21 gigawatts to travel through time. And a single gigawatt is enough to power 110 million LED lights, or is equivalent to the power of 1.3 million horses, according to the U.S. Department of Energy.

Global crypto mining consumes about 114 terawatt-hours a year, which is more than the annual electricity needs of the Netherlands or the Philippines, according to a tool built by researchers at University of Cambridge Judge Business School’s Centre for Alternative Finance.

Indoor cannabis farms also use heavy amounts of electricity to power lights, fans, water pumps and heating systems. U.S. cannabis farms consumed about 1% of national electrical power in 2012, according to a study by the Lawrence Berkeley National Laboratory. Today, that would be equivalent to nearly 40 terawatt-hours a year.

Write to Paul J. Davies at paul.davies@wsj.com and Caitlin Ostroff at caitlin.ostroff@wsj.com