It does have a Royal Brierley label, (I've just looked at the enlarged second pic, doh!
I have never seen a bit of Caithness like this, and I do see a lot of it around (being in Scotland helps).
There are a couple of mistakes I
've found in the 20th century book. There's a bit of Mdina described as Isle of Wight Studio Glass - thankfully, in the cropped image on the front page it was part of the cropping!
And Ed Iglehart does not live in Cumbria, in England, but in Palnackie in Scotland.