Hi Martin,
"he accepts they existed in 19 C. England"
A bit later than the 19th century Martin - as a MacAlpine's worker my father encountered them regularly in the 1940s/50s - "no dgs, no blacks, no Irish".
I believe I had one of them pointed out to me as a child in (of all places) Liverpool, but I either was unable to read or did not understand their significance.
Have actually worked as an electrician in pubs in London where Irishmen have been asked to leave - this would have been in the early to mid 1970s
Jim Carroll