A total of 10,000 litres of fake vodka, branded as Glen's, and more than 35,000 litres of pure alcohol enough to make 100,000 litres of vodka were seized by the 70 Customs officers who took part in the bust, called Operation Baygood.
Customs officials estimated the alcohol confiscated would have defrauded the Treasury out of £1m in duty and VAT if it was sold on the black market.
The bootlegged booze contained higher than average levels of methanol, which can be fatal if consumed in large doses.
"The success of this operation is a result of our determined efforts to disrupt and dismantle the illegal supply of alcohol," said Andrew Pavlinic, assistant chief investigation officer at HMRC. "This was a substantial and sophisticated production, bottling and distribution plant with the infrastructure to distribute large quantities of counterfeit Glen's vodka throughout the UK."
It took the officers two days to dismantle the equipment in the factory, at a farm near Little Dalby in Leicestershire. Six men have been arrested.