I'd like to point out that Watson is not in costume -- she's worn that top before when waiting to go into hair/costume & make-up.

I wonder if that's Clemence stood next to her or just a minder. Whoever they are, they have an envelope of photos in their hand. I remember getting an envelope just like that.

I agree that's Rupert's double, but it's not stunt, just body. They use them to check the light and camera angles caue the actors who are under strict time laws don't have time to do stuff like that.

But the double was wearing the same clothes as Rupert -- they wouldn't dress the twins the same as Rupert for a scene.