Etudiant,
It is the mad cap world of an internet hoaxer known as Sorcha Faal. He/She simply picks a news story and spins it.
From the Yorkshire Post
No local media organisations were issued with any such notice.
SONIC BOOM: Conspiracy website says drama was start of WW3 as UFO shot down after rising from sea - Yorkshire Post
These newspapers denied (in virtually identical articles[42][43]) that the British government had issued a Defense Advisory Notice prohibiting their publishing the facts of this event that Faal had alleged
https://en.wikipedia.org/wiki/Sorcha_Faal_reports