IF you want an encounter with one of Britain's mystery big cats then your best bet is to head for Dorset. There are more sightings per head there than anywhere else in the country.

Merrily Harpur, one of the UK's leading investigators, celebrates this fact in her new book, Roaring Dorset: Encounters with Big Cats, launched this weekend at the Dorset County Show, which is being held at the Dorchester Showground.

Author of the best-selling Mystery Big Cats of 2005, Merrily has now turned to focus on her home county – aptly, she lives at Cattistock, near Dorchester – with a gazetteer of sightings over the decades and a round-up of the latest thinking on the strange phenomenon.

"Dorset has a huge number of sightings going back to the 1960s," she told me. "I wanted to bring out the book before my file got any fatter and the book became too heavy to carry around!

"Thousands of people throughout the UK and hundreds in Dorset have seen big cats resembling black panthers or pumas, as well as sometimes lynx-like animals and others resembling the Scottish wildcat."

A freelance cartoonist, illustrator and writer, Merrily has been fascinated by the big cat mystery since she heard about the Surrey Puma when growing up in that county in the 1960s. "An encounter with a big cat has been called Britain's most common encounter with the unknown, and it is the unknown because these big cats are a mystery," she said.

"People assume they are the descendants of animals released when the 1976 Dangerous Wild Animals Act came in, but there's too much evidence against it. It's one of those mysteries that, the more you know about it, the more mysterious it gets, and I'm afraid it's true that anyone who wants to research big cats comes up against too many stone walls to really find an explanation."

Merrily favours the "daimon" theory, an idea going back to Ancient Greece which envisages an intermediate being, both material and non-material. "They have one foot, or should I say paw, in this world and one in the Otherworld," she said.

"Everybody scoffs at the idea because we are 21st-century people and we don't believe in that sort of thing. But these creatures have been believed in for many centuries in the form of fairies, elves, goblins and so on.

"For want of better evidence, I think that these creatures might be traditional daimons appearing in a new form geared to attract the attention of 21st-century people who don't believe in them – part of the Otherworld teasing us."

■ Roaring Dorset is published by Roving Press (www.rovingpress.co.uk) of Frampton, Dorset, at £4.99. For more on big cats, and to log sightings, visit Merrily's website, which is at www.dorsetbigcats.org -

HEAR more from Merrily Harpur and Jonathan McGowan on my Mysterious West podcast. Listen at www.westerndailypress/mysteriouswest and on Glastonbury Radio (www.glastonburyradio.net).