suggest they pool their resources, whatever they happen to be, meal plan, batch cook etc. like a family would. perhaps send him a few student cook books. there's a lot of them about for inexpensive and easy recipes.
there's also plenty of £1 meal cookery books, and the Jack Munroe ones are very good for ways to make tasty things out of cheap ingredients (the one I've got was written from the aim of recipes based on the sort of things you get in tins and packets from food banks)
to be spending that much, there are probably a lot of ready meals involved, so help him learn how cheap can also be easy, and with batch cooking you basically have a freezer full of ready meals.
it's nice that he's wanting to help his friend out, and sharing their food costs for home cooked, budget friendly food, he'd still be able to do that, but still spend less. also worth asking if there are cheaper supermarkets nearby, or making sure he's buying own brands rather than just automatically grabbing the famous ones at eye level.
also, encourage things like eating more veggie meals, as they are cheaper. and things like tinned green lentils are great for bulking out anything you make with mince.
in fact, whenever I make a chilli, I don't even use mince anymore at all. I use a tin of green lentils, a tin of kidney beans, and a tin of mixed taco beans instead. it's even more filling than with mince, so goes further, and makes a lot of servings for very little cost, so plenty to freeze for another time. you can have it with rice, chips, nachos, jacket potatoes, in a burrito, all sorts of ways.