These guys are really talking about mass deaths.
Quite simply there are too many of us to go back to some airy-fairy magical hippy agrarian wonderland.
In roman times, italy had a population of about 11 million with Rome having a population of one million. Italy is about the same size as the UK.
Assume we are just slightly more knowledgeable than the Romans and maybe we could have 10 million on our little island with less than meditarranean climate conditions. So the other fifty million have to bugger off elsewhere.
Fact of the matter is, even if we all volutarilly agreed to be skint, we need five out of six of us to be dead, unless we use the evil magic technology.
Luckily the tech is here, despite what the neo-luddites say.
The magical market pixie dust has (just in time) produced scientific advances in batteries so that we may continue to be stuck in commuter traffic (in little yellow electric cars) on the M4 till we are due to don cloth caps and collect our inflated-to-nothing pensions in 2040 or so...
And the leccy can come from windmills, nuclear, wave, solar panels and, wait for it... COAL!!!
Right then. Down the winchester.