Like the title characters Reggie and Ronnie Kray, Leslie Grantham (Nipper Read) was a convicted murderer. He murdered the West German taxi driver Felix Reese in Osnabrück, Lower Saxony on December 3, 1966. He was convicted of murder in 1967 and sentenced to life imprisonment but only served ten years.
Producer Jonathan Sothcott has had this story in development for some time. At one point he reportedly had Martin and Gary Kemp lined up to co-direct it and cameo as The Kray twins.