A man was found hiding in sewers below a trap door before being arrested in a drugs raid in Hornchurch.
Safer neighbourhood officers executed a search warrant on Thursday (March 7) at a commercial garage at the rear of Billet Lane.
Officers forced entry by cutting the locks and found around 295 cannabis plants, with an estimated value of around £295,000.
They also discovered a bed, extensive lighting equipment, tea making facilities and a microwave, suggesting someone was living inside.
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The Met Police said the officers initially believed no-one was present in the garage but they saw a mobile phone ringing at the site and concluded otherwise.
A spokesperson for the force revealed they discovered a trap door in the toilet floor and a man found hiding inside the sewer area.
He was arrested on suspicion of cultivating cannabis and was wanted on recall to prison.
The premises, police added, has been secured and all plants will be seized while the investigation is ongoing.
Inspector Mark Connolly said: “It is a fantastic result in our efforts to disrupt organised crime groups who are operating across Havering.
“You can report any concerns you have around drugs or drugs supply anonymously via Crimestoppers on 0800 555 111."
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