Great notes Baxuss. Nice to see another collector of vintage queens! The Mauritius portrait is by Pietro Annigoni. The Queen bought the portrait in 07 but I think it was originally painted for the Fishmongers guild. "I did not want to paint her as a film star; I saw her as a monarch, alone in the problems of her responsibility" he said. Maybe some think that's overly romantic or nostalgic but I think it makes for a great artistic vision. Plus I think it captures, perhaps unintentionally, the modern need for monarchy and other ceremonial/historic institutions to retain the pride and dignity of the "head of state" position thus denying it to other parts of the government--hopefully keeping them more humble, as it were.
There's 2 varieties, one by TDLR and one by Bradbury Wilkinson.
This is a great little guide for collectors of Queens, I've used it many times:
http://www.pjsymes.com.au/QE2/default.htm
Annigoni is portrait no. 9.