A British Airways letter in the National Archives in London recounts an embarrassing incident on February 9, 1980, when a bodyguard attempted to carry a gun onto the Concorde supersonic airliner in London. British Airways refused to allow it, and tense discussions ensued, before the bodyguard eventually gave up the weapon. It was shipped back to Thailand separately.
The reason the letter appears on green paper is that it is a censored copy: the original has been withheld from the archives and replaced with a green copy with some passages blacked out. This was done to remove the name of the person whose bodyguard attempted to carry the gun onto Concorde: it was Thailand’s crown prince, Maha Vajiralongkorn.