Julian Rathbone

Julian Rathbone was a prolific author writing in a number of genres in addition to the crime novels discussed here.

Jan Argand

Pluto published two of the the three Jan Argand novels. Strangely Watching the Detectives, the last novel was published first with Introducing Commisioner Jan Argand on the cover. This was followed by The Euro-killers the first novel. The correct sequence is

The Euro-Killers
Base Case (not published by Pluto)
Watching the Detectives

The passage of time and earlier events are discussed in the novels and (sort of spoiler) reading the two Pluto ones in their sequence gives a different reading to events.

Elvis Costello

Given that Rathbone wrote another book called "Accidents Will Happen" and mentions "Olivers Army" in another book "Trajectories" I assume the naming is deliberate.