The novel is a fictional reworking of the true events surrounding the murder of a policeman carried out by Harry Roberts in 1966 - (the event behind the football terrace chant "Harry Roberts is our friend, he kills coppers). Because he takes as his inspiration real events and real characters, Arnott's work (much like the American writer James Ellroy) taps into some sort of popular collective history.
Of course the danger of populating his drama with Soho gangsters and bent coppers and so on is that they could easily end up being little more than being cliched and generic and obvious, and you could end up with another example of the dull witted crime capers that were produced in the last decade and in this. But Arnott, again like Ellroy, is so much better than many of his peers. In Arnott's trilogy ("The Long Firm
The books really are a cracking read, I wish there was more telly like the BBC's "The Long Firm" and I hope the ITV series does justice to "He Kills Coppers"