For 50 years, the British government secretly investigated and dismissed hundreds of UFO sightings while hoping to convince the public that these mysterious objects were weather balloons or meteorites. Yet flying saucers have been a source of controversy and fascination ever since, inspiring rock stars, artists and Hollywood films. As top-secret government files are due to be made public for the first time, this programme asks how UFOs suddenly appeared in Britain in the 1950s and why the government was so keen to keep its investigations under wraps. As light is shed on the web of secrecy that has shrouded Britain's X-Files until now, can the rational explanations used by the sceptics stand up to scrutiny?