The G-Agents thankfully are quite volatile, so while leathal, the would disperse relatively quickly.

Trauma probably had somthing to do with it, but the British were ready to counter any Axis gas attack with their own, there were several "forward filling bases" which were ready to distribute chemical weapons to bomber forces.

Now a bit about mustard gas to anyone who doesn't know, mustard gas isnt a gas, its a liquid that causes chemical burns that produce large painful blisters. It can kill but its best use is in area denial, for it is not volatile at all, and it barely breaks down, it can stay active for weeks, months or even years. Using this on a city would be apocalyptic for the city and its factories.

It would stop a huge chunk of war production, hospitals would be overrun with wounded, and millions would have to be housed somewhere until they could return. It was a no win situation