Where’s all this additional electricity going to come from?
Exactly

I was told a few months that if a 1/3 of us switched to electric vehicles tomorrow - the National Grid would "trip out".
You were being told porkies. Not least because if we were to cut gasoline consumption by 1/3, the need to refine fuel would also drop by 1/3, releasing the enormous amount of electricity to be available for other things like charging EVs.