In his book "Blood of the Isles," (Saxons, Vikings and Celts in the US) Bryan Sykes tells a nice story about two brothers who lived near Tregaron, mid Wales, during the 1950s and 1960s. They were well known in the local area as "Neandertals" and often received visits from school children who were being taught about human evolution.
Of course, Sykes didn't really believe they were Neandertals but presumably the two brothers had unusual physical traits that may have resembled archaic humans.
Interestingly, 20 miles north of Tregaron, are the Plynlimon Mountains where Physical Anthropologists in the early 20th century believe they had discovered an isolated, relic population.
Described here by Carelton Coon:
In the first place, the work of Fleure and James on the Plynlimon moorlands people of Cardiganshire, an isolated group who live for the most part as shepherds, shows that this region is the center for all Wales of the greatest concentration of brunet dolichocephaly; their work also indicates that a primitive human type, with large browridges, a low vault, a projecting occiput, sloping forehead, a broad face, and prognathism survives here, and is to be found in solution throughout most of Wales. That this type is a survival from pre-Neolithic times seems reasonable. The head lengths associated with it run well over 200 mm., in many cases over 210 mm., and the stature is usually under 170 cm. The moderate stature, the narrow vault breadth, and the brunet pigmentation, as well as the general morphological character, prevent this type from being closely associated with the large-headed northern Palaeolithic sub-stratum in Ireland; one is reminded rather of the early Combe Capelle skull, and to a lesser extent, of the Mesolithic men of Téviec in Brittany.http://www.theapricity.com/snpa/chapter-X3.htm
Futhermore, in his book Sykes also claims to have found a very old cluster of y-dna Haplogroup I (he calls it Wodan) in mid-Wales, suggesting a link with the relic populations identified by anthropologists.
This "old" Y-dna Haplogroup I is also found in north-east Scotland and is associated with the ancient homeland of the Picts.
I understand there is a subclade of y-dna I that is said to be very old in Britain?