EA:-
Why is it that the cover up has been so well executed ?
Because the MOD is simultaneously; the accused, the judge, and the jury of its own case, and because many professional aviators (ie many members who post on this very forum) don't understand the difference between serviceability and airworthiness, and can't be bothered to discover it.
In that respect I again highly recommend David Hill's excellent book, Their Greatest Disgrace. In telling the tale of the deaths of the 29 occupants of Chinook ZD576 on the Mull of Kintyre in 1994, he explains that it was grossly unairworthy, why it was grossly unairworthy, why that unairworthiness was not limited to that aircraft or fleet but spread like a canker throughout UK military aviation which it infects to this day, who caused it, and how they have been protected by a cover up by the RAF Star Chamber ever since. The answer to your question is in the book, EA.