The savings in CO2 emissions for the likes of rapeseed, sunflower etc per MJ of energy is only around 50% compared to diesel. You have to release a lot of CO2 to grow these crops intensively. And that’s before you even consider where the land for these crops come from, potentially chopping down CO2 absorbing rainforests in many sorts of the world.

Biofuel from Used Cooking Oil is worthy considering for sure, but the quantities possible are tiny compared to the petrol/diesel we use.