We also tax those already.

EDIT: There is a fixed VAT charge of 5% on electricity, as well as a currently 16% levy on electricity to cover various environmental and social benefit schemes. Which is hilarious, as the UK is moving away from fossil fuels for its electrical generation mix, while taxing electricity consumption much more than it taxes gas (5% VAT and 5.5% levies). This punishes those using electricity for heating and incentivizes people to continue using gas at home. This is on top of the fact that currently, gas is much cheaper (in unit rate, per kWh) than electricity. It's like they can't make up their mind on what they want to accomplish. For fuel, the tax is currently just under £0.53/L with 20% VAT added on top of the total as well.

Exactly. Why do we need to come up with clever formulas to estimate car CO2 production based on car's gross weight, wheelbase, engine displacement, efficiency ratings if it's much easier to calculate how much CO2 is produced from the car's fuel?

PS: electricity is hard as there's a lot of volatile renewables, but I bet is still way easier than clever formulas.

Tax them again!