This promotion is available in various stores, view all products to get the cheapest Diet Coke. If you'd like to find out whether this product has a bigger discount in another store, check the category 'Supermarket'. You may also find these offers interesting: Diet COKE, Diet COKE & Diet Coke.
Your best option is to purchase this product at Morrisons. Of course you can also take a look at the leaflets of other stores. If you click on Supermarket under categories, you will find similar stores to Morrisons.