I would be surprised if the practice lasted as long as the 1940s, Steve. I would have thought all the jobs that became open to women as a result of the lost generation that died in WW1 would have ended the practice before the 1920s, if it hadn't died out earlier.
But then I have been known to be wrong...
Even today in the fruit/veg picking areas of Kent and East Anglia gangmasters are bringing over what are virtually refugee slaves (Kurds, Bosnians etc)to work illegally on some farms for a pittance.
RtS