Biggus, if you are talking of known unairworthiness, then no such aircraft, military or civil may be permitted to fly in normal circumstances (abnormal ones being the "at war" scenarios that have been postulated).
The point being, of course, what is known and who by? The provision of airworthiness is an arcane and complex procedure that requires deep technical knowledge as typified by tucumseh's valuable contributions to this and other threads. It is sadly not typified by the MOD in whose stewardship we have seen that depth of knowledge stripped away as professional engineers who were wont to say "no" were replaced by the technically unqualified who could be relied upon to say "yes". With due respect to the MAA that lack of experience and depth of knowledge still pertains and there is no slick answer to it. The first and most urgent step though is to remove it from the pressures and influences that have reduced this vital arm of Military Flight Safety to the state we are in today. In parallel with that is the failure of BoI's over these decades of decline to face up to and expose this scandal. Again the answer must be to remove Military Air Accident Investigation from within the MOD/Services to without. Painting new signs and doors achieves nothing more than a false sense of security.
Just to emphasise, this is all about the provision and maintenance of airworthiness and not of serviceability. For all I know the Sea Kings, the Chinook, the Tornado, the Hercules and the Nimrod (all mentioned earlier and the subjects of individual threads within this Forum) could well have been serviceable pre-flight. My claim is however that they were not airworthy and/or fit for purpose, and that was known of by those whose duty it was to ensure that only airworthy military aircraft be Released to Service into the three Services. They failed in that duty and 62 people died in the subsequent airworthiness related accidents.
Self Regulation Never Works and In Aviation It Kills!