[King of Snake]

Rick is the main "songwriter" and producer in Underworld, I think he has the final say in whatever gets made or not. But of course Karl will also write stuff and they will bounce ideas back and forth, possibly now also with Darren Price although I don't know to what extent. Same with Emerson, although it seems he was not quite so involved with the actual writing and production but this is hard to tell.

From the radio 1 interview a few years back:
Rick: "we are not democratic, we don't work that way. If you believe in something you follow trough and make your point until everybody understands."

in this interview Karl also describes it as a conversation, which would start with a piece of music (by Rick) and then he would "reply" and try and get a response to that again ("yes" "no" "indifferent" "keep going")