Be careful that you do not compare tailpipe emissions of ICE vehicles with co2 from electricity used by EV or PHEV cars.
The industry compares 'well to wheel' emissions to identify the environmental impact and there are many reports on the internet. Of course using renewable electricity has the lowest impact and a lot of EV drivers buy green electricity and/or generate PV electric.
To fully charge an Ampera/Volt from empty takes (according to Vauxhall) 12.7kWh, transmission losses are about 2% which takes that figure up to a round 13kWh.
According to today's earth.org.uk figures, if you had charged your car last night between 1am and 5am the average emissions would have been 408g/kWh, i.e. 5.3kg
If you charged it instead yesterday evening it would have taken 491g/kWh, i.e. 6.3kg CO2
There are probably an infinite number of ways to combine those figures but:
At best a battery range of 50 miles with 5.3kg/charge is 106g/mile. A worst case for battery is 30 miles with 6.3kg/charge which is 210g/mile.
For petrol, best case might be 50 mpg which is 286g/mile. My MX5 does nearer 30mpg i.e. 477g/mile.