ps: you may feel you're earning money for free, but you tend to pay more on the item in the first place because Amex only rebates to you because they charge more to retailers to process their payments, so retailer has to raise their prices to make a decent profit margin, nothing in life is free.
I find that with lidl you have to know how to shop there. I save about £40 on my shop compared to Morrisons. There are some items I know I won't get but as long as I am organised I can buy them on a monthly basis. Their none branded cereals are great and far cheaper and generally I find their fruit and veg great too.
I do Lidls and Aldis too. Some stuff is much cheaper (although if you buy basics it wont be). Cheaper than branded. I buy ketchup, mayo etc, milk, eggs, flour, spread, jam (in square pot like luxury branded), fruit and veg, loo roll, meat and sliced meat, crisps and yoghurts. I find Aldi better but that's because I get more stuff there.