We average about £100 per week for a family of four (plus diapers, not including fags). I've recently started shopping online and can often meet or beat that £100, including fags and delivery charge.
I'm finding that I'm spending far less online because I don't 'see' things and say 'Ooo, I want', plus if I can't remember if I need something, I just pop in the kitchen whereas if I were at the store, I'd buy it just to be on the safe side.
On average, I'm saving around £20-30 by shopping online.