It’s hard being a London black-cab driver, but it’s even harder to become one, thanks to the infamous exam known as “The Knowledge”. In this one-off documentary, we follow several wannabe cabbies taking The Knowledge, including a former bus driver, a Kosovan immigrant and a single mother. As well as the personal stories behind those being examined, there is also the entire issue of passing The Knowledge itself: it is so hard 70% of all candidates drop out. Mind you, it is not surprising that so many people fail given how much they need to learn. Over an average period of four years the candidates need to learn over 25,000 streets and thousands of landmarks. It almost makes you want to feel sympathy for when a cabbie refuses to drive you south of the river for seemingly no reason at all. The Knowledge: World’s Toughest Taxi Test is on Channel 4 at 21.00.