I live out in the boonies and I know that our only 2 grocery shops do home delivery. I haven't had the need to use it, but it's nice to know it's there just in case! Tesco delivers, but charges £5, I think. You can shop online with them. Somerfield delivers, but there's no online shopping -- you have to go to the shop and do the shopping and then they bring it home to you. But I have an aunt who doesn't drive who uses their service and loves it. She has no problem getting to them on the bus, but would never be able to carry bags of groceries home.
So it's definitely not restricted to London!