A secret tunnel leading to a reported £40 million underground cannabis farm has been found in the basement of the old Broadway Theatre in Deptford.

Police uncovered the drug farm after they were called to a residential house on Tanner's Hill on 1 October following a reported break-in.

There, underneath the property, officers said they discovered a "large number of cannabis plants along with the equipment used in the cultivation of cannabis," estimated to be worth around £40 million in total.

Three men, aged 28, 45 and 47 and a 36-year-old woman have been arrested on suspicion of the cultivation of cannabis, and have all since been released under investigation.

The Daily Mail reported that the cannabis farm is estimated to have been making over £4 million each year, with the farm likely having been operating for around a decade.

A neighbour reportedly said they had been oblivious to the situation, but described having heard "what seemed like drilling", but "never for very long".

The criminal gang behind the tunnel are believed to have tunnelled down beneath the toilet inside the Deptford house until they reached the large abandoned basement.

The gang then tapped into the mains power supply using underground cables connected to the former theatre, which was converted into flats in the 1960s.

A Met Police spokesperson said: "At this time, there remains a police presence on scene whilst access is facilitated to the site through a specialist entrance at ground level to ensure the safety of the officers undertaking the investigation."

The spokesperson added that there was increased police activity around the old Victorian theatre, and that temporary structures were being erected, but police were working with the local council to minimalise disruption and there was no cause for concern.