Right at the beginning of the movie, we see James McAvoy in his wet underwear, with a clear bulge.
There are several other bulge scenes later on also.
50 minutes in the movie, James McAvoy only wearing a short undresses in front of the camera. He is slightly remote, so we don't see a lot of details.
We can however see that James McAvoy has a great bubble butt and a rather large uncut penis.
We see again his butt when he is making love to a woman, 74 minutes through the movie.