The British Government has released thousands of pages of files documenting thousand of UFO sightings, and even apparently documents about UFO “policy.” These files were compiled over a some 50 years by the Ministry of Defense.
Here is a brief story about it.
Here is where you can actually look at the documents – the page recommends downloading rather than just opening them because of their large size. There is also a summary of the files’ ‘highlights’ here in pdf format.