At first when I finished the film I thought he was lead because altho the story was about Iris, he was in every scene with Judi Dench and had an immense presence. Then I opened Letterboxd to log the film and that’s the sinopsys I saw there:
“True story of the lifelong romance between novelist Iris Murdoch and her husband John Bayley, from their student days through her battle with Alzheimer’s disease.”
So, the film is indeed about Iris and John. Conclusion: he is lead in all possible ways. Another case of category fraud in the 2001 Supporting Actor race alongisde Ethan Hawke’s.
He should have been nominated in Lead for this film, and in Supporting for his turn in Moulin Rouge!. He still would have a fair shot of winning Supporting Actor since he won BAFTA.