So how would this radical new system work in practice? How much would motorists actually pay? Would petrol still be taxed, too? And could you cheat your way around it?

Those are the questions Nick and Felix set out to answer in episode three of our second series.

Their new book - Critical Mass - explores the concept of taxing cars by weight and miles driven, not by type of engine.

Oliver's here to 'stress test' their proposition, and see if their answers really stack up.