We all have a favourite supermarket, and the likelihood is you head there pretty much every time. You might shop there out of habit or convenience, but you can make huge savings by being open minded about where you do your shopping.
It might be that you're just as happy with food from Lidl, Aldi, Asda, or Morrisons as you are with Marks & Spencer or Waitrose. Your loyalty to one shop might be holding you back from better deals at another.
There are also some great discount codes available if you're happy to become a supermarket nomad. I switched from Sainsbury's to Waitrose, which sounds like my shop got more expensive, but they were offering £20 off a shop over £80 for a total of five shops — that's a massive savings of £100. I'll switch again when the next code comes up.
Comparison: You can use MySupermarket to compare prices at different shops and to transfer your favourites from one online retailer to another.