Oh, sorry.
I think it was similar to how U2 does it: I think Kele came in with the basic strong structure, riff, melody, whatever, and then all 4 of them would finish writing the song together. I'm pretty sure Matt was in charge of his drum parts and Gordy was in charge of his bass parts/keyboards/etc.
But, from everything I've read or gleaned over the years, I felt like they said the albums were always a full band product by the 4 of them. Every one of their album to date have the writing credits listed as all songs written and composed by Bloc Party.