Despite the success of the 1987 BBC documentary series, The Duty Men, the failure of the 1986 series The Collectors made it hard for the BBC was unwilling to contemplate another Customs-based drama series. Independent producer Paul Knight was looking for a follow-up to his successful ITV series London’s Burning. He told reporter Annie Leake that, “I realised there were tremendous possibilities there for a fictional series. In many cases HMCE’s powers far outreach those of the police. It’s surprising that the BBC didn’t spot the potential first.” By a strange coincidence, one of the London’s Burning directors was Keith Washington, who had also worked on The Collectors! Writer Anita Bronson based the scripts for The Knock (named after the call-sign for a raid, and consciously echoing The Sweeney) on extensive research. Inevitably, some of the scenes recall The Duty Men. A “classic-bag-switch” in the penultimate episode seems very much like a scene from the BBC series, right down to...