Victoria Hannan looks at the lives of London's cabbies.

Brought to you by Hailo, the taxi app. Download free from iTunes and Google Play.

• 

  Mark
  In his 20s, Mark got fed up of working in accounts at BT. So he got up at four in the morning, every day for three years so he could do The Knowledge before work. Twenty-four years later, he still thinks it was the best decision he’s ever made.