Is it a bird? Is it a spaceship?
No, it's a secret US spy plane
<em>The Guardian, Saturday June 24, 2006</em>

It is the stuff of internet conspiracy theorists' dreams. A top secret, hypersonic, cold war spy plane that was allegedly flown by the Americans in UK airspace without the government's permission.

Publicly, the UK government played down newspaper stories about people who reported seeing UFO-like phenomena. But documents released under the Freedom of Information Act suggest the Ministry of Defence took the rumours much more seriously. Its investigations even threatened to strain the special relationship. "It does show that they were concerned that this thing did exist and the Americans were flying it around willy-nilly over the UK," said David Clarke, a social scientist at Sheffield Hallam University, who obtained the documents. "It certainly suggests that the British government suspected that they were being kept in the dark."

Continues over at <a href="http://www.guardian.co.uk/science/story/0,,1804926,00.html" target="new">The Guardian</a>