Okay I'm always trying to economise at the grocery store. But, the best I seem to be able to do is around £150 per week. We have three adults and two kids (18 months and 3 1/2 yrs) in the house. I shop at Tesco, and I don't buy overpriced kiddies foods (like disney yogurts or Thomas pasta, etc.) I don't buy already prepared food (unless it is for me to take to work for lunch because it is cheaper than buying lunch at work).
If you live in greater London, how much do you spend on groceries? Am I going wrong somewhere?