Police in the U.K. have stumbled across a cryptocurrency mining operation after raiding what they thought would be a cannabis farm.

The police authority for the West Midlands metropolitan county forced entry into the industrial park unit on May 18 in Sandwell near Birmingham and found around 100 devices apparently used for bitcoin mining, according to an announcement Thursday.Officers found that the operation was stealing "thousands of pounds worth" of electricity, "It's certainly not what we were expecting!" Sandwell Police Sergeant Jennifer Griffin said.The raid came after reports of multiple people visiting the unit at odd times of day and night, and "lots of" of wiring and ventilation ducts. A police drone had detected a considerable source of heat."They are all classic cannabis factory signs," the announcement said.The unit was unattended at the time of the raid and no arrests have been made as yet.The discovery is only the second such crypto mining farm encountered in the West Midlands, according to Griffin.