Hard to say, but don't forget that the UK's famous outbreak in the Royal Free Hospital, London in 1955 led to the creation of the name myalgic encephalomyelitis, and the modern understanding of the characteristics of this disease. So I would have though that ME was already well known in the UK.
Yeah I forgot about the Royal Free Hospital outbreak in the 1950s. ..thanks ... as I said in one of my other posts here that there was outbreaks of ME around the world in the 1950s.. ALL over the world as outbreaks then were reported in so many different places. I would have to say world wide there was a ME epidemic going on at that time.
Whatever you want to try to attribute to causing ME/CFS.. would of had to be going on back then.
Can you relate to whatever you think lead to an increase in the 1980s.. to an increase in the last couple of years of the 1940s to mid 1950s after which these outbreaks seem to have died down again? Also ask yourself why did this die down?? (could it just be a normal viral pattern? or was something which was triggering this off stopped???)
I personally think the environmental factors is just something which knocks the body around to make it more susceptible to whatever ME is. No not causitive as such. I also think there is many different things which are making us more susceptable, not necessarily just chemical exposures.