The title says it all really.
Great writer is our Robbie but I'm wondering if Gary Barlow allowed him to write for Take That.
Yes.
Robin Williams is credit as writer on the album Nobody Else in 1995.
On the song Sure.
Written-By – Gary Barlow, Mark Owen, Robbie Williams
Note also that when he came back in the album Progress in 2010 he was credited in all songs:
Written-By – Barlow* (tracks: 1 to 11), Donald* (tracks: 1 to 11), Orange* (tracks: 1 to 11), Owen* (tracks: 1 to 11), Williams* (tracks: 1 to 11)
From Wikipedia:
Williams explained that the long-standing feud between himself and Gary has been resolved, and how close they now were.
