These will be the best sources.
Jo Whiley: Johnny Marr Sofa Sessions - Jan 13, 2022.
Someone kindly put all the Marr bits together from Jo's 1.5 hr show.
At 13:25 - Bigmouth.
With "...now I know how Johnny Marr felt..." added.
Thanks to the kind person messaging me about this.
There's 6 variations of this in the archive (video & audio) with one being attributed to a master tape.
Another for vinyl collectors, but superb versions exist of this digitally if not.
... The moods, the twists, the precision … it's difficult to do well, and I was blessed with a most supremely intelligent producer. He played and sang backing vocals on every track … so beautifully … and brought something that no one else could hear into each track...