I'm pretty sure the sign on the building says Cowper St. According to my 1954 Bartholomew's, Cowper St ran from Summer Lane to the east and ended in a kind of t-junction, the southern branch of which was a dead end, the northern branch leading to Geach St. The map doesn't make clear if the short arm of the t-junction is Cowper or Geach St, if you see what I mean. I remember that area quite well.
G