The clue is in the name.

The publication by the Ministry of Defence of their files on UFO sightings has reignited the debate about whether or not UFOs exist.  And the answer is, of course they do - if you see something in the sky and nobody can identify it, then it's an Unidentified Flying Object isn't it?  Simple.  The question of whether it's being flown by little green men from Mars or wherever is a separate issue - and indeed if it could be proved that it was, it would no longer be a UFO, would it?