Russell is a most interesting man in his own right, and in this performance he also serves as a gramophone. He reproduces several of Gladstone's (1809-1898) phrases. He clearly imitates Gladstone's velvet deep bass. Russell's own aging, unsteady voice is replaced by a very sonorous, completely different one.
Psychologists did an experiment: they offered people who could not draw to copy a Picasso drawing, a portrait of Stravinsky. It came out terrible.
Psychologists turned over the drawing and offered to copy it again. And here it came out much better! Because people copied the meaningless lines they saw, they didn't try to copy the image that was sitting in their heads. You have to be an artist to represent the image in your head, just as you have to be an essayist to formulate a thought on paper.
This is why Russell speaks better when reincarnated as Gladstone. He suddenly returns to his youth, when Gladstone was to him someone great, misunderstood and fearful.
This is not a split personality. It's not acting. It is a journey of personality within himself, the most fascinating of all possible journeys.