British Gas engineers entered the Grand Posthouse in Lichfield Street earlier this week and discovered the operation in the cellar. West Midlands Police was called, and officers spent the next few days emptying the building of drugs.
The Grand Posthouse, a Grade II listed building, is a few minutes' walk away from a police station in Bilston Street.
A spokeswoman for West Midlands Police said: “Around 1,000 cannabis plants were discovered in the cellar of the Grand Posthouse in Lichfield Street by British Gas workmen on May 3. No arrests have been made. We were alerted by a utility company."
Forensic investigators and a specialist cannabis removal team were photographed removing bags of cannabis from inside the building.