It is four years since Alastair Humphreys left England to cycle the world for charity. Having braved the freezing Siberian winter, only the baking desert of Turkmenistan now lies between him and the familiar sights of Europe.

Many people may be unsure as to what the area of Central Asia (or Turkestan) actually covers. The five independent states of Central Asia - Kazakhstan, Turkmenistan, Kyrgyzstan, Tajikistan and Uzbekistan - form the core of a diverse area of natural beauty and striking terrain that stretches to parts of western China and Afghanistan.