Around 30 police officers, including dog handlers, swooped on the Drakelow Tunnels, in the shadow of the Kinver Edge beauty spot, at Wolverley, on the outskirts of Kidderminster.
They discovered a network of hydroponic equipment, including heating, lighting and ventilation fans, as well as the plants, at the complex, which in the Cold War was designated a centre for local government leaders to set up HQ in the event of a nuclear attack. Officers swooped on the site at around 9am yesterday.
Earlier, officers from West Mercia and Warwickshire Police executed a search warrant in a dawn swoop on an address in Kidderminster, where a 45-year-old man was arrested on suspicion of money laundering and being concerned in the production and supply of controlled drugs. He has now been bailed.
A quantity of cash was also seized at that property.
The tunnels have for decades housed dark secrets – from being a mysterious government nuclear bunker to, more recently, hosting ghost hunts in the dead of night.
The latest find – which shocked neighbours – comes at a time when plans have been submitted by the company Quercus Ilex SA to create a museum and gift shop and to build six new homes in the grounds.
Drakelow Tunnels were used to manufacture machine parts during the Second World War and it was in the late 1950s that the site became the regional seat of government for any nuclear strike.
The 285,000sq ft tunnel network stretches for about three miles and much of the original government equipment is still there.
North Worcestershire police Supt Kevin Purcell said: "While executing the warrant at Drakelow Tunnels we discovered a large and sophisticated cannabis growing operation and although the plants will need to be tested it would appear that this seizure has prevented a large quantity of illegal drugs ending up on the streets. That in itself is a very positive outcome.
"While we have made an arrest in connection with this I would stress that this is a dynamic, ongoing investigation and we would very much like to hear from anyone who may have seen any suspicious activity near the tunnels or know anything that could be helpful to our inquiry."
Supt Purcell said the operation had presented 'significant challenges' due to the sprawling nature of the tunnel system.
The search had to be carried out over a large area and the aim had been to cause as little disturbance as possible within the complex, he said.
After the police find, workmen from Western Power dug up and disconnected a suspected illegal electricity supply to the tunnels complex. One woman living nearby, who did not wish to be named, said: "A neighbour phoned me about 9.30am and asked what I'd been up to as there were police down the lane.
"They I saw police and dogs, a riot van, four or five marked cars, four unmarked cars and police racing around the compound.
A guy from the electricity company then knocked at the door and said someone had been up to no good in the tunnels – they'd been growing cannabis."
She said she had seen recent 'comings and goings' at the site by a van.
"Locally people had been joking about the tunnels being a good place for someone to grow cannabis – but it turns out to be true."
. The complex includes a sickbay, security booth and the 'BBC Room', where broadcasts would have been made telling people what was happening after a nuclear attack.
Anyone with information that could help the police inquiry is urged to call 101.
Details can also be left anonymously at Crimestoppers on 0800 555 111.