Children's Encyclopedia
Arthur Mee edited the Harmsworth's Children's Encyclopedia & Atlas, published in 1922-25 in 10 volumes (7412pp). He then republished it himself through the 1920s & 30s; this is believed to be from c1939.
Scale correct at 9.0 miles/inch, or 1:570,000. Grid squares of 5 miles are printed across the map, and a scale of 60 miles = 168mm.
Everything stops abruptly at the county borders.