Police discovered underground bunkers containing £500,000 of cannabis after a raid at a Lincolnshire farm.
The pre-planned raid at the farm in Skendleby near the east coast on September 3 led to searches over nine days after four bunkers made up of shipping containers were found 20 feet underground.
Their entrances were concealed within barns and in total 12 shopping containers were used to make up the bunkers.
They housed a large number of cannabis plants, with officers estimating the drugs would have a street value of £580,000.
More than 300 tonnes of illegal waste, a shotgun and six stolen cars were also found. 22 horses and one llama were found at the farm itself in a poor condition and were taken away by officers.
Three men, aged 34, 35 and 28 were arrested on suspicion of production of a Class B drug, burglary with intent to steal, animal welfare offences and possible waste offences.
The 34-year-old was also arrested on suspicion of possession of a prohibited firearm and theft of a motor vehicle.
The three suspects were also interviewed in relation to this activity before being released on police bail while instigations continue.
Officers will return to monitor the safe removal of the waste in the future, which is expected to cost those responsible up to £100,000.
Detective Superintendent Rick Hatton from Lincolnshire Police said: “We are extremely grateful to our counterparts in Spain and our partners for assisting with the exploration of this site.
“With the operation being underground we have needed some real specialist support to uncover this activity.
“Only with the skills of those who joined us from Lincolnshire Fire and Rescue, the Environment Agency, East Lindsey District Council, RSPCA, Dyno-Rod and the Home Office’s Defence Science and Technology Laboratory have we been able to get to this point.”
Officers, drone support and the dog unit arrived at the farm, accompanied by officials from the Environment Agency who had intelligence to suggest waste was being stored illegally at the site. Officers from the Spanish Civil Guard also joined the operation.
The seven Environment Agency officers found approximately 300 tonnes of baled waste, 60 part-dismantled vehicles, used asbestos roofing materials, household rubbish and mixed manufactured wood. Evidence was also found of six separate areas used to burn waste illegally.