How Does Aldi Keep It's Prices so Low? (Aldi vs. Lidl)

I'm not seeing the price advantage nowadays compared to a few years ago personally but I don't really buy much in the way of alcohol. Their bakery section is just low grade parbaked products same as convenience stores, full of yeast and certainly not healthy but still very tasty I'm sure. There is also the issue that a higher percentage of the goods they sell are imported many of which would be cheaper to buy from abroad than from UK suppliers. I pretty much shop at all the main supermarkets, all have their advantages and disadvantages.