Thanks for the replies, they're much appreciated. Incidentally I took a decision to use real names in the book, since it covers the period before 1900. I'm glad I did, as descendants of some of the "scuttlers" whose exploits are described are beginning to get in touch.
At a recent book signing at Waterstone's on Deansgate in Manchester I met two of the descendants of Owen Callaghan, a "scuttler" who was convicted of manslaughter in 1887. He was sentenced to twenty years penal servitude for the fatal stabbing of a "Bengal Tiger" named Joe Brady. His descendants were able to tell me what became of him in later life, which helps me to fill in one of the gaps in the story.
Andy