Jack Merritt, a student from Cornwall, spotted the animals which have been extinct in southern Britain since at least the 1960s Pine martens recorded in West Country by night-vision camera | World news | The Guardian
Three possibilities: 1) A previously un-noticed population which has survived the past few decades - this is the most unlikely option. 2) Natural spread from the known population in South Wales - this is almost as unlikely given there is quite a large area between the two points. 3) Illicit reintroduction through translocation of animals from one of the existing populations - this I suspect is the correct option.
I know that particular area very well. It is largely open farmland, and while the cliffs and some small bits of moorland and along the coastline could be described as scrubby, its really not that 'wild'. There are a few blocks of Forestry plantation but not a lot. I would say almost certainly this(these?) animals were artificially brought here.
