Plug-in hybrid vehicles (PHEVs) operate in the same way as standard 'self-charging' hybrids, recovering energy under braking and storing it in the battery. However, a PHEV will only add a few miles under common driving scenarios. And this means you need to recharge the battery via a plug to appreciate its full benefits when it comes to fuel economy and performance.

I ran a Volvo XC40 PHEV for six months and got 90+mpg with a full charge. But when the battery was empty this dropped to just 33mpg. You can read about my PHEV experiences in my long term report, here: www.honestjohn.co.uk/our-cars/volvo-xc40/