GTAT: was it not the case until recently that any delay leaving theatre WAS lost from R&R time and not tagged onto the end?
RE: Tristars. I recall an interview in Flight International some years back where the top neddy at Cathay Pacific was asked if his "old" Tristars caused problems for the company. His replay was that there was no such thing as an "old" aeroplane, just those that became increasingly expensive to keep young!
The procurement bods at MoD would do well to heed those words - there are only two real choices: either buy the spares that are needed or replace the aeroplanes with new ones.
In the past, of course, the RAF has benefited from BA operating aeroplanes that were older and had more hours than the military versions. The VC10 was a great example: when something broke on a BA one, the RAF got advance notice.