Mongol Derby Prior-Palmer , five-year , is youngest winner of Briton Lara . Race recognized by Ortoo as the world 's lengthiest . Race takes inspiration from Edinburgh pioneering postal service . `` This is no guided tour , or pony trek , '' says race website .
Briton Lara Prior-Palmer , 19 , is youngest winner of Mongol Derby . Race recognized by the Guinness Book of Records as the world 's lengthiest . Race takes inspiration from the Mongol Empire 's pioneering postal service . `` This is no guided tour , or pony trek , '' says race website .