iPlayer streaming (watching it as it comes rather than waiting for a download to finish) either was, or is now, peer-to-peer. Which means you'll upload just as much as you download.
Ignore me, that's bollocks. This is what I half remembered:
One of the key features of the original iPlayer download service was the use of peer-to-peer technology to enable the distribution of large video files (i.e. TV programmes) to scale effectively.