They Stalk by Night written by Nigel Brierly in 1989 and is now considered to be a classic in British big cat circles.
An excerpt from the introduction to Nigel Brierlys book by Dr. F.A. Turk.
Professional zoologists are usually wary of acknowledging the existence of BIG CATS, in the wild, in Britain. Roaming quiet fields and dense thickets, nocturnally nomadic, making their kills at night, evidence for them is, not surprisingly, mostly anecdotal; their sighting but momentary.......
Mr Brierly has taken much time and more trouble to collect, record, plot and examine sightings and evidence in a most factual manner. He is an enthusiast, yes, but a most temperate, controlled, and perserverant one. We can trust him; he is no headline seeker but an informed amateuer who will spare no trouble to establish the truth........
My belief is that, so reasonably and temperately does he present us with his evidence, that we must do more than take the subject seriously. I believe 'beast' watchers would do well to take this little book as a guide of the most reliable kind, for collecting and presenting their own findings in whatever part of the country they live.....
Altering for a moment one of the more memorable of the late Bernard Shaw's obiter dicta, I would say "I recommend you all to buy Mr Brierly's book. Buy it, read it and then - act upon it." Believe me, you could not have a brighter lamp to light your labours.
Dr. F.A. Turk
Formerly University Reader
Hon. Research Fellow
University of Exeter