Good on Channel 4 for airing this (with full knowledge that it would be politically unpopular in the UK) but the login requirement seems like either a huge oversight or a crude practical joke. Maybe this was a restriction put in place by the video's creator?
I suspect I wasn't the only one to create a new throwaway account on 4od to watch the video this morning.
[1]https://twitter.com/tombrossman/status/415816279992172544