1kg mince, the cheap fatty one, you can easily just take the fat off once you brown it. And then some 35p(ish) passata
Half of it for spaghetti bolognese, bulked out with frozen veg as frozen veg is much cheaper.. Frozen sliced peppers, a mixed veg that has stuff like courgette etc in it.
Other half for chili con carne, can use the frozen peppers, and then two 30p tins of supermarket basic kidney beans.
Cheapest pasta I have seen would be Sainsbury's or asda own brand, they're, I think 30-40p for 500g, to go with the bolognese sauce, and £1 rice.
Bag of 1kg carrots, the cheapest ones will be under £1, usually the basic own brand or "wonky" veg. Grated, it can be added to sauce in bolognese and Chilli, and it just melts away so you don't see it in there and can't taste it, but it really bulks it out.
1kg of chicken, I usually get from the butcher at £2.50, but I'm sure I have seen supermarkets regularly have offers at the same price for fresh and I have seen very cheap frozen.
The rest of the carrots, rice, add potatoes (again, wonky veg variety to make it cheaper) for chicken with rice potatoes and carrots, if you have any frozen mixed veg left that can be added although I'm not sure how it tastes because I do think it's better in a sauce and you can't tell the difference as much. Can also get things like tinned sweetcorn or peas for around 30p
Own brand milk
There should be leftovers from the above 3 meals, that you can then turn into something else. Can buy cheese and make some sort of pasta bake with the bolognese leftovers. Cheese is more expensive but you can get own brand again. Sometimes, grated is cheaper too when it's the basic one.
Fajitas or something with the leftover chilli and the cheese.
Cheap bread isn't that nice for sandwiches sometimes, but for toast it's usually fine, so can get that for breakfast. Own brand basic jam for 35p and own brand butter.
If you already have some flour at home, can make pizzas too. Can just buy yeast for around 70p.
Also, there are a few websites that you can type in whatever you have in your cupboards already and they'll give you some meal ideas for what you already have. Google, there are a few sites.
If you can stretch to an extra couple of £, and look online, the main supermarkets often have offers like £8 off £40 for new customers etc. Even Amazon prime now, and Amazon fresh do this. That is for delivery only though. That way, you'll get more food and can maybe even thrown in some own brand snacks like yoghurt.