The Ministry of Defense just released approximately 40 pdfs of UFO-related documents dating back to the 70s.
The documents, uploaded to the national archives by the MOD, contain police reports from witnesses claiming to have sighted UFOs or other extraterrestrial activity.
The MOD points out:
"As previously stated the MOD's only purpose in looking at reports of UFOs is to establish the presence of a matter that might be of a defense concern, such as unauthorised aircraft in UK airspace."
While most eyewitness reports seem to be sent in a few times over before ever receiving a reply, the MOD, even when responding to sightings with more than one witness, deliver a polite, yet stern, "We are satisfied that there is no corroborating evidence to suggest that the United Kingdom's airspace was breached by unauthorised aircraft."
Although these documents may not have been what every sci-fi fan was hoping for, there still are plenty of interesting reports on UFO sightings, crop circles, and alien abductions. You can peruse the national archives here.