Brat Farrar - Josephine Tey

Uhm, does anyone know in which time period this is set in? This novel has been published in 1949, but the gaslightning in the street of London kind of threw me off. That plus the fact that whole story feels like it is set in the 1920s.

I have read the short Tey biography in the front of my edition, so I know that she has written this book way before the actual publication date.