first off, learn the joy of the various staple carbohydrates. Enough rice to feed you for a day costs about 5p and cooking it pretty much consists of putting it in hot water. Learn to use these as the core of your meal with the rest of ingredients to add flavour and
Typical foods good for this include rice, pasta, lentils, potatoes, noodles etc.
learn how to make some cheap simple sauces from scratch to add to these. A tin of chopped tomatoes and some italian herbs makes a quick, cheap (about 20p a head for a big plate of pasta and sauce) and healthy dinner. Make big batches and freeze them so you can just microwave them and stick them over rice or pasta etc.
work out how to get the best out of special offers, especially to stock up on things you would be buying anyway. But on the flip side, don’t be tempted to buy something because its on special offer without checking its actually a bargain first.
Supermarkets usually put a hefty discount on things going out of date (especially if they bake fresh bread etc. in house, they practicly give it away an hour or less before closing). Its still good food and can usually be frozen so it’ll keep a long time.
a bowl of cereal makes a good meal, especially since its around 30p even for a posh cereal.
don’t eat out unless you really have to. £10 for a pizza is hard to stomach when your hard on cash and know you could have made enough food to last you a week for the same price.
going vegetarian can be a cheap option since meat is so expensive. Lentils have half the protein density of steak, but at about a twentieth of the price.
and don’t skimp on the vegetables. Make sure you’re getting a wide variety of fresh made foods (and aren’t deep frying it all in lard then serving it on a bed of salt) you don’t have to worry too much about nutrition too much.