It's always been bizarre that casting directors apparently find Gina McKee attractive.
She single-handedly ruined The Forsyte Saga by being infamously miscast.
Jason Clarke filled that role in this series. He looked ridiculous. Like an actor in a low budget stage production.
Jason Clarke is basically miscast in anything he appears in. I was so disappointed when he turned out to be Potemkin.
Complaints about Gina McKee's attractiveness are misplaced here, I don't think she's meant to be sexpot in this role. I can't speak to her other roles besides the general defense that she's generally pretty in that kind of slender, bloodless British way, and probably still good looking enough for a woman in her mid-50s.
If McKee has any problems, it's the same shared by many British actresses of her type. They're not unattractive, but they lack a kind of broader "sex appeal", which really I think is of a broader, non-British kind of sex appeal. Given how many slender brunette female British actresses of basically the same type seem to get produced in Britain, I suspect its that non-British people are looking for something more voluptuous or something.