Cannabis plants worth £1m seized in Welwyn Garden City by police

550 plants were discovered at the property in Howardsgate

More than 500 cannabis plants with a street value of £1m have been seized by police.

A drugs factory was discovered in Howardsgate, Welwyn Garden City, on 14 December, and Hertfordshire Police said officers were also treating it as a "modern slavery" inquiry.

The building's mains supply had been tampered with, the force said.

A 42-year-old man from Hatfield was arrested at the scene on suspicion of producing a controlled drug.

He has been released under investigation.

Police arrested a man at the scene

Sgt Paul Brown said: "The cannabis factory is being treated as a case of modern slavery and we have been working with the Salvation Army in relation to safeguarding those involved.

"The devastating impact of drugs cannot be underestimated and this case completely highlights that."

The building was no longer a "fire and safety hazard", he added.