Gangsters who ran the UK’s largest plot to grow cannabis have been convicted at the Old Bailey.

The group produced industrial amounts of the drug, which was estimated to have had an annual yield of more than £26 million.

A total of 16,428 cannabis plants were seized at a number of locations across the county and Norfolk between 2013 and 2015.

A total of 15 offenders have now been convicted following an investigation by Kent and Norfolk Police. Two people were found not guilty by a jury.

The group operated from sites in Rochester, Sittingbourne, and North Walsham in Norfolk.

Each location was set up in an almost identical manner, with each having purpose-built two-storey wooden constructions which had been created inside industrial units.

The layout and equipment used was also identical.

The first factory, in Rochester High Street, was uncovered on June 28, 2013 when police went there following reports of a burglary at the location.

The back door had been forced and police discovered a large cannabis production inside.

Enquiries showed that the premises had been leased since 1st December 2012 to James Allen.

The investigation identified that Allen, Michael Edward Corcoran, Michael Jay Corcoran, Stuart Sollis and Stefan Henderson-Clarke had been linked to a premises known as the ‘old taxi rank’ in the Canal Basin, Gravesend, since early 2013.

The investigation identified that between 2013 and 2014, the crime gang had rented a further three industrial units at the site, using false details.

During this period further members of the group had become involved in the conspiracy, these included David Graham, Stephen Macey, David Heath, Colin Walls and Andrew Prowse.

Garry McIntyre and Ellie Corcoran were also suspected to be involved but were found not guilty of the offences.

In the early hours of Wednesday 17 June 2015, officers were called to a disturbance at the site and on arrival Michael Edward Corcoran was seen driving away from the area in his Range Rover.

A small cannabis plant in a pot was discarded on the floor nearby.

As a result of this discovery, police raided the first industrial unit, which was found to consist of several rooms constructed from chipboard.

Officers went on to find a large cannabis production with four separate growing rooms. Plants were at various stages of growth.

A later inspection showed the electricity supply to the unit had been tampered with and the meter had been bypassed.

The estimated loss of revenue for every 30 days has been estimated in excess of £5,000.

When the first unit was searched, it was noticed that cables ran to a second unit next door.

The warehouse was raided the next day and a significantly larger cannabis production was found.

This building consisted of a large double sized warehouse with a large, secured gated yard.

Two vehicles were found within the yard that showed links to Michael Edward Corcoran.

A later inspection showed this warehouse did not contain an electricity meter, the unit had been illegally connected to the power supply causing an estimated loss of £14,805 for every 30 days the cannabis factory was active.

"This was a highly organised and prolific conspiracy to produce and sell cannabis on an industrial scale" - DI James Derham

On June 19, 2015 a further raid was carried out at a third industrial unit.

This unit comprised another large warehouse with a parking area.

A Ford Transit was parked outside the unit which showed connections to Michael Edward Corcoran and Andrew Prowse.

An inspection showed the electricity had been tampered with and the meter had been bypassed.

It is estimated that £44,585 in revenue was lost for each six-month period that the unit was operational.

A total of 9,888 cannabis plants seized from Canal Basin.

The whole setup was capable of producing a crop four times a year. The potential annual street value of these drugs would have been in excess of £16m.

In Norfolk, a address called The Laundry Loke Unit was leased for a seven year period on October 9, 2014 by David Graham using false details.

As a result of police surveillance, in partnership with Norfolk Police, Michael Edward Corcoran, Graham, Macey, Terrance Murphy and Stephen Creed were seen at the Laundry Loke warehouse in late 2015.

On October 26, 2015, a warrant was executed at the address by Norfolk Police.

The premises had been divided into numerous rooms that contained equipment and cannabis grows. A total of 1,907 plants were seized. The potential annual street value of these drugs would have been in excess of £3m.

An electrician confirmed the power supply been tampered with and the meter bypassed and the total estimated loss of electricity was in the region of £30,000.

In Sittingbourne, Graham leased a unit at the industrial centre for a five year period on May 1 2015.

The investigation showed Michael Edward Corcoran was also involved in obtaining the lease and on December 14, 2015, Stephen Macey was observed to leave the unit and get into a white Ford Transit which was parked outside.

Police then executed a warrant and when officers entered, they found Alan Marquiss, Damon Mills and Christopher Marsh inside.

A total of 4633 cannabis plants were found, with a potential annual street value in excess of £7.5m.

All those convicted are due to be sentenced at the Old Bailey in July 2017.

DI James Derham, Kent and Essex Serious Crime Directorate, said “This was a highly organised and prolific conspiracy to produce and sell cannabis on an industrial scale.

“We estimate the annual street value of these plants was in excess of £26 million – a significant amount of money that could have been used to fund further criminal activity.

“This case was a significant undertaking by the investigation team due to the level of sophistication and analytical work.

“This case sends out a clear message that Kent Police has the resources and expertise to offenders involved in high level, organised criminality to justice.’

DI Tom Smith, from Norfolk Constabulary, added: “This was the largest cannabis factory ever discovered in Norfolk during a joint operation with Kent and Essex Serious Crime Directorate.

“The operation was complex and time consuming but demonstrates that organised crime and drug trafficking networks operating in Norfolk will be targeted and closed down.

“These convictions also highlight how forces across the country work together to tackle organised crime.”

The defendants are:

James Allen, 39 and of Woolwich Road in Abbey Wood, London, pleaded guilty to five counts of conspiring to produce cannabis and three counts of abstracting electricity.

Stephen Macey, 25 and of Commercial Road in Paddock Wood, pleaded guilty to five counts of conspiring to produce cannabis and five counts of abstracting electricity.

Christopher Marsh, 30 and of Ethelbert Road in Margate, pleaded guilty to one count of conspiring to produce cannabis and one count of abstracting electricity.

Damon Mills, 18 also of Ethelbert Road in Margate, pleaded guilty to one count of conspiring to produce cannabis and one count of abstracting electricity.

Michael Edward Corcoran, 51 and of Mount Avenue in Yalding, was found guilty of seven counts of conspiring to produce cannabis and five counts of abstracting electricity.

Michael Jay Corcoran, 28 of Odo Rise in Gillingham, the son of Michael Edward Corcoran, was found guilty of four counts of conspiring to produce cannabis and four counts of abstracting electricity.

Stefan-Alex Henderson Clarke, 27 and Kennedy Walk in Walworth, London, was found guilty of four counts of conspiring to produce cannabis and four counts of abstracting electricity.

Stuart Sollis, 51 and of Bowyer Street in Camberwell, London, was found guilty of five counts of conspiring to produce cannabis and four counts of abstracting electricity.

David Heath, 48 and of Wentworth Crescent in Peckham, London, was found guilty of three counts of conspiring to produce cannabis and three counts of abstracting electricity.

Colin Walls, 52 and of no fixed abode, pleaded guilty to one count of conspiring to produce cannabis and was found guilty of two further counts of conspiring to produce cannabis and three counts of abstracting electricity.

Terrance Murphy, 47 and of Caspian Way in Purfleet, Essex, was found guilty of one count of conspiring to produce cannabis and one count of abstracting electricity.

Stephen Creed, 45 and of Beccles Road in St Olaves, Great Yarmouth, was found Guilty following of one count of conspiring to produce cannabis and one count of abstracting electricity.

David Graham, 50 and of Plaistow Lane in Bromley, pleaded guilty to five counts of conspiring to produce cannabis and five counts of abstracting electricity.

At this trial, Alan Marquiss, 69 and of Disraeli Road in Thamesmead, London, pleaded guilty during proceedings to one count of conspiring to produce cannabis and one count of abstracting electricity.

Andrew Prowse, 32 previously of Southampton Way in Camberwell, London, pleaded guilty during proceedings to three counts of conspiring to produce cannabis.

Ellie Louise Corcoran, 21 and of Commercial Road in Paddock Wood, was found not guilty of three counts of conspiring to produce cannabis and three counts of abstracting electricity.

Gary McIntrye, 36 and of Alfred Road in Brentwood, Essex, was found not guilty of three counts of conspiring to produce cannabis and three counts of abstracting electricity.