Think this getting a little off topic now but...
External moderation generally does not do a lot more just a check ensuring the standards are decent across the Uni, they might make a few recommendations but these are often just trivial things.
agree PhD marking and competition is not the reason for % of 2.2's not to mention how strict PhD marking is generally, its like any other academic job...
Yes PhD's would actually increase student marks i think slightly.
I think the marks may more be where each faculty places the quality line/mark, generally over the last few decades the number of 1st's & 2.1s have increased dramatically, maybe Notts just hasn't kept pace with the inflation level of grades at other Unis. Unfortunately i think this has happened due to employers only being interested in 2.1 level students meaning grades are becoming less & less relevant (something the QAA & DoE needs to correct), but the reality is if your a good student you'll get a 2.1 wherever you go.