Well said Engines.
MoD's letter presupposes only MoD had a copy of the documents. This is seldom the case. Design Authorities are paid to retain insurance copies of much of the airworthiness audit trail. The same contract maintains the safety case. Lord Philip knew what to do. He simply got in touch with retirees who had followed instructions and kept their own copies of documents they'd signed. This won't be possible with all documents, but the rules allow one to make an engineering judgement on the evidence available.
MoD will go to extraordinary lengths to perpetuate the lie. On a number of occasions I've reached the situation above, only for MoD to claim the produced documents do not exist - so they must be forgeries. On one unforgettable occasion a Gp Capt even denied the existence of the aircraft under discussion, when his department (in AML at RAF Wyton) was caught red-handed destroying files. We fell about laughing as there was a photo of the aircraft on the wall behind him. (Nimrod R). At the same meeting, it was put to him that his department had actually scrapped Reference Systems (fundamental to functional safety and, hence, a valid safety case). His reply was that the company (GEC-Marconi Secure Systems in Basildon) had stolen them and the police should be called. GEC promptly produced the letter telling them to break down the rigs and return them to 14MU, and the resultant delivery notes. You really can't make this stuff up.