Leon Smart during his 18th 'appearance' to be tested for 'the knowledge'. During the examination prospective black cab drivers are tested on their knowledge of London's streets. They are given a starting point, an end point and a mid point, they then have to work out the route and explain it exactly with street names, direction of travel, left hand turns, right hand turns etc to the examiner. Mr Smart has been doing the knowledge for four and a half years. He failed this 'appearance'.