Who is Dunford Lipsey from The Modigliani Scandal and what is their importance?

Dunford Lipsey is a detective. Lampeth hires Lipsey to find the lost Modigliani. He travels to Paris, where he finds the owner of the fish shop and the old man who told Dee about the Modigliani. He then moves onto Italy, where he meets Dee, Mike and Julian. Lipsey comes up with one of the copies of the Modigliani, that he proceeds to pass on to Lampeth.