Get the latest entertainment news, reviews and star-studded interviews with our Independent Culture email Get the latest entertainment news with our free Culture newsletter Get the latest entertainment news with our free Culture newsletter In the early Nineties, Her Majesty’s Customs and Excise was losing its battle with the country’s drug gangs. Heroin was flooding in from northern Pakistan, through Turkish and north London crime networks, and onto the streets. Overwhelmed and seemingly out of options, the Investigation Division did something nobody saw coming. At the behest of Margaret Thatcher, they recruited a small team of their own officers, gave them false identities – “legends”, in the trade – and sent them deep into the criminal underworld. These were not trained intelligence agents. Not police detectives. They were customs officials, used to checking suitcases and occasionally confiscating Scotch. Barely overseen and with limited funding, these undercover narcs ended up seizing more than 12 tonnes of heroin, with a street value of over £1bn. If this sounds like the plot of a thriller, that’s because it …