Green’s Dictionary of Slang

to chatter on pointlessly, thus n. witter, meaningless chatter.

1971		N. Smith Gumshoe (1998) 121: ‘Stop wittering, lad,’ he said wearily.
1981		W. Boyd Good Man in Africa 164: What is he wittering on about? Morgan thought.
1992		D. Jarman diary 12 June Smiling in Slow Motion (2000) 144: Tony Peake wonderful company and listened to me ‘wittering on.’.
2000		N. Griffiths Grits 183: Wuh laugh. An then just witter on about all kinds uv shit.
2008		S. Lewis Bad Traffic 10: [A] middle-aged woman addressed him in a witter as meaningless as birdsong.