Well first of all ... The British have always trailed us in just about everything!!!
So to hear they used SO2 up until 1940 is not a surprise.
SO2 was used as a primary refrigerant in small systems in the early days of mechanical refrigeration in this country.
For example. An apartment complex in Hollywood CA had a central compressor and they ran lines up to each room where the fridge was hooked up.
When you had to service the fridge, a repair tech would go in, use his pair of pinch off tools and isolate the circuit. Make his repairs and solder back together the lines. Then he would use his pinch off tools to round back the copper tubing and return the device to service.
Of course there were also home refrigerators which used SO2.
There were stories by guys who worked the industry back then about birds dying in people's homes, plants dying when exposed to the fumes, .... if the serviceman vented the stuff outside the window, even a tree would be killed by the stuff.
And to think of fosgene gas as being dangerous ... that's nothing compared to SO2 in any amount around anything living!!!
From what I understand, it is still available for sale today.
Although I have no clue what someone would use it for.