Former British paratrooper Karl Bushby wants to use the Channel Tunnel to return to the UK after a 28-year journey [Getty Images] A British adventurer has been refused permission to use the Channel Tunnel to complete his 36,000-mile walk around the world. Former paratrooper Karl Bushby, 57, set off from Chile in 1998 and has reached Belgium. Under the terms of his challenge, he is unable to use transport.