I feed 3 of us on £40 a week so I think it would be very tight, however most of our meals serve us twice, if that makes sense? I have 2 freezers so batch cook or buy big packs and freeze.
Sausage casserole. Bulk with chickpeas, red lentils, baked beans, tinned tomatoes. Cut the sausages up and you'll find you use less sausages per head than you would if they were whole. Serve with rice.
Frozen fish to make a fish pie. Don't use prawns (or buy the tiny ones as they're cheap) and it's a pretty cheap and tasty meal.
Cottage pie. Bulk with lentils, frozen peas and frozen carrots.
Curry. Use a jar if you don't have spices. Again bulk with lentils, and do a mix of chicken, veg and potato.
Buy chicken legs/thighs, much cheaper than breast.
A really cheap meal which is one of my favourites is this www.bbcgoodfood.com/recipes/313611/ovenbaked-egg-and-chips but rather than tomatoes, I serve with beans.
If you normally have weetabix, etc - buy store brand rather than branded. Meal plan today for the whole 23 days. Breakfast, lunch & dinner. Don't deviate. Before meal planning, go through every cupboard, the fridge & freezer and write a list of what you already have.