Yesterday, in a South Wales oak/ash woodland, I came across a tree with hundreds of small holes about 1cm wide in the bark, all the same size and evenly spaced, and resembling shallow pits rather than insect exit holes. They started below head height and went up at least 20 feet. The closest thing I have seen to this was an acorn woodpecker larder, or holes made by a sapsucker, but obviously these were in USA, not Wales. I have never seen anything similar in UK, though I have seen lots of woodpecker holes. Can any UK woodpecker species produce holes like this, or is there another explanation?