R.I.
And the full Latin style was:
Sua Maiestas Victoria, Dei Gratia Britanniarum Regina, Fidei Defensor, IndiƦ Imperatrix.
In the Latin style "Britanniarum", the plural genitive of Britain, or "of the Britains", was (and is) used instead of the UK of GB & I!
Edward VII adopted the designation "Britanniarum omnium rex", King of All/Every/Both the Britains, which strangely still seems to be the usual Latin style, although the state's Latin name is just Britanniarum Regnum, with the literal translation "Coniunctum Britanniae Magnae et Hiberniae Septentrionalis Regnum" a secondary option.
In contrast the Emperors of all the Russias was in Latin, as in the original Russian, usually styled "totius RussiƦ Imperator", Emperor of All Russia, in the singular.