Aldi and lidl are considerably cheaper, but in some ways a false economy! We shop at aldi then end up having to do a second shop for things we can't buy in there such as cosmetic stuff, some kids snacks and some cleaning products, because of the limited choice. We've just worked out that between those two shops we spend about £80 which is the the same as we would have just going to the usual supermarket. Also I've found their dates on food are a lot shorter and stuff seems to go off quicker so we end up rebuying some things. Also you have to look past the prices, for example squash seems really cheap but morrisons own is nicer and 2 for £2 so is actually cheaper! Aldi is fine if you know what you want but not very inspiring otherwise. We're going to start doing online shopping again because we saved much more that way as there's no browsing and you have to be organised which means you save money anyway!
As ooh said, aldi definitely have got more expensive though, more and more of their finest range is on the shelves and although nice the prices are becoming on par with other places. Although I will continue to shop in there just for nappies and wipes because we've always used them, they're excellent and you can't beat the price!