So an EV is on par in CO2 emissions with a modern diesel if all the electricity generation is from coal. The UK average for 2017 was 292 g/kWh which is around a 14% improvement on that, a bit worse than I expected but that's what the data says. What this ignores however are the expected future trends in generation mix (more solar and wind are being built right now and lots of coal plants are scheduled to close within the next decade), and also the air quality benefits (NOx, particulates, etc.) of concentrating emissions in a few stationary (and therefore not weight limited) locations where it's more cost effective to deal with than millions of tail pipes in city centres.
In Europe much of the push for electric vehicles is driven from the latter consideration, air quality in a lot of cities is poor.