Three Britons were jailed on Friday for running a huge cannabis farm inside a former Cold War nuclear bunker in an isolated area of southwest England.

The gang used the bunker, built in the 1980s to house local government officials in the event of a nuclear attack, to cultivate more than 4,000 cannabis plants capable of producing 2 million pounds ($2.6 million) worth of drugs a year.

The bunker, located in Chilmark near Salisbury, was no longer owned by the Ministry of Defence but was still intact with its nuclear blast doors in place which made it almost impenetrable, police said.

The men, who were arrested in a midnight raid in February but only after they had left the site, also locked workers inside so they could tend to the plants 24 hours a day.