Which mode of transport has the lowest CO2e per kilometer in the UK?

This was a bit odd.
I was digging through the UK’s official CO2e numbers looking at the environmental impact of different transport modes. The old favorites are at the top of the list – air travel and the “Chelsea Tractor”.
What surprised me was the bottom of the list. I’d expected to see a BEV or rail travel, but no. It was the Chelsea Tractor again, albeit in plug-in hybrid guise.
Intuitively you’d think a BEV like Tesla or the Nissan Leaf would have a lower CO2e per kilometer because of renewables, economy of scale in generation etc. Not the case, allegedly, because of the stored CO2e in battery production, plus the marginally more efficient generation from the engine.
The PHEVs have smaller batteries and therefore less stored CO2e to carry around.
Not that I’m advocating we all rush out and buy Mitsubishi Outlanders to save the planet (other PHEVs are available). I’m pretty sure that BEV number is going to come down as we get better at extracting, refining and recycling batteries. And it doesn’t account for the zero emission benefits to local pollution levels.