Also look at other ways to save money to free up more for the treaty end of food. Best price for gas and electricity, that sort of thing. If you live alone, your water will probably be less on a meter unless you're in a very low rateable value property (this seems to be a random number - our water rates doubled from our first house to our second even though the house value was about the same - it turns out the first house was unusually low rates because it was a back to back with only a tiny amount of outside space and didn't have an indoor bathroom when it was built, which was still reflected in the rateable value).
You can eat and drink well for £20 pw for one person but it takes work and it helps if you can average this over time by buying bigger packs or multibuy offers - eg tinned tomatoes, beans etc are often much cheaper in multipacks than single cans, but you need to buy 4 in one go, which needs space and a bigger outlay, but if you can do it for the things that are commonly on offer, the savings over time can be significant.
Look at the reduced counter.
Use cheaper shops, especially for toiletries and cleaning products - these can be much cheaper in Wilko, Home Bargains etc than the more expensive supermarkets.
Make use of your freezer if you have one, as you can split family packs into individual portions and batch cook.
Watch what you waste - make this as low as possible. Also think about how much you use. Some people on here talk about using what seems to me like alarmingly high amounts of toilet paper and cleaning products. The woman who spent £30 a month on kitchen roll was a particular highlight. People regularly talk about using a whole shower gel per person per week, that sort of thing. To me this seems mad.
Look for cheaper alternatives - frozen fish and berries instead of fresh, normal brocolli instead of purple sprouting, for example.
There's no need to spend £10 on a bottle of wine or £5 on a bar of chocolate for it to be a treat, how ludicrous. There's lots of lovely stuff at a fraction of that price, especially in the likes of Aldi or Lidl.