I think the ones credited to a sole composer, such as Trick and Moon, will have both music and lyrics by that person.
I've read that Banks is responsible for RA&B's lyrics (as well as the bulk of the music) and that he was aiming to continue PG's style of quirky/humorous story-telling lyrics. There are some tricksy rhythmic bits in the song that I'm guessing are the Collins-generated components.
By the way I like how in your post the two guitarists get the first-name treatment while the other two are surnames-only, which is my preference - I shudder slightly at the first-names thing.
Haha oops, I didn't notice that until now. I think I prefer that for some reason.
And I figured that Banks wrote the lyrics as well, I mean it'd be hard to write clever humorous lyrics, I just didn't think Phil would write those kind of lyrics (then again the man wrote the impressive lyrics to Inside & Out and Scenes From A Night's Dream, so who cares what I say).