A lot of American actors I work with are in character all day long. You can't talk to them. It's Method and the whole thing.
Ellis Peters's historical detail is very accurate and very minute, and therefore is not only interesting to read but good for an actor to acquire a sense of the period. And the other thing I think is that an actor lives in the land of imagination.
There is no reality of consciousness independent of the effects of various vehicles of content on subsequent action (and hence, of course, on memory).