About 100 machines were found at an industrial unit at Sandwell in the West Midlands, with thousands of pounds of electricity reportedly stolen to continue the operation.
Officers raided the site on May 18 after obtaining a warrant when evidence suggested it was being used to grow cannabis.
This included dispatching a drone and seeing higher than normal temperatures in the complex.
However, upon entering the unit, they discovered the machine bank, complete with a bird’s nest of cables and heat exhaust ducts.
West Midlands Police officers believe the network was being used to extract the cryptocurrency Bitcoin.
In order to “undermine” a Bitcoin, a computer has to perform complex calculations that require a lot of time and electricity, thus generating a large amount of heat.
The magnitude of the energy consumption required for Bitcoin mining around the world has been noted as an environmental concern.
A single Bitcoin is worth around £ 26,000 at the time of writing, although the price is notoriously volatile.
In a statement, West Midlands Police said: ‘We heard how many people were visiting the unit at different times of the day, many cables and ventilation ducts were visible and a police drone picked up a source of considerable heat from above.
“These are all classic cannabis factory signs – but when the agents walked in they found a huge bank of around 100 IT units as part of what is considered a Bitcoin mining operation.
“The computer equipment was seized and investigations with Western Power revealed that the power supply had been bypassed and that thousands of pounds had been stolen to power the ‘mine’. “
Sergeant Jennifer Griffin said: “It’s definitely not what we expected! It had all the hallmarks of a cannabis grow op and I think this is just the second such crypto mine we come across in the West Midlands. “
She added, “We have seized the material and will seek to seize it permanently under the Proceeds of Crime Act. No one was in the unit at the time of the warrant and no arrests have been made – but we will inquire with the owner of the unit. ”