I have only 'involved' in one accident which was many years ago (G-BDAN) and involved by virtue of being on shift.
Long before the media were aware of the accident the shift supervisor was instructed to remove all the records for this a/c from our filing system.
At that time we retained all records for a month before parceling everything up and sending it to Tech Records which were then at Lasham. So while I am not aware of a requirement it seems to be practice.
Usual disclaimer that someone will know better !