Officers forced entry to the unit in Bradford Street at 9.45am on Thursday and found a sprawling cannabis factory across three storeys.

A total of 3,112 plants were recovered.

Police say it is one of the biggest they have discovered in recent months and they suspect it was being used to fund organised crime.

Three Vietnamese men who are believed to be in the country illegally were arrested at the premises and later charged with cannabis cultivation.

The men, one aged 26 and both of the others 36, were due to appear at Birmingham Magistrates Court on Friday in connection with the find.

Police also found the electricity supply had been bypassed to power the extensive lighting and extraction system – and a trench dug into the road to tap into the mains.

Cannabis disposal team manager Mike Hall said: “This was a really extensive set-up, not the biggest we’ve encountered but certainly up there in terms of scale.

“We received intelligence suggesting the property was being used as a drugs factory and acted quickly on that information to execute a warrant.

“We always value information like this and take it seriously – if anyone suspects a property near them is being used to cultivate drugs then please get in touch.

“Cannabis factories like this are often linked to organised and violent crime, tend to attract anti-social behaviour, and are serious fire risks because of the way electricity is bypassed and the dodgy wiring.”

Anyone with information is asked to message West Midlands Police on live chat through the force's website or call the charity Crimestoppers anonymously on 0800 555 111.