Definately more vegetables. Every meal revolve around protein, vegetables, and fuel in the form of either a starch or fat, depending on your specific diet. If your schedule doesn’t leave time for whole food then fill the gap with a shake.
So, as a practical matter, I’d replace the porridge with eggs, and lots of them. Lunch would be chicken breasts, broccoli and rice. Cook it the night before and put it in tupperware. Dinner would be Salmon and veggies with olive oil. Like that. You don’t have to eat the same thing everyday, just follow the Protein/Veggie/Fuel model, and plug in whatever you got.
As far as buying food on a budget, I don’t know if yall have price clubs in England, where you pay a yearly membership fee to buy bulk items at a discount, but they are well worth the price of membership. Over here they offer the best prices by far on the staples of eating big and eating clean. Tuna, Chicken Brests, Olive oil, Frozen Veggies, Eggs, Cheese, fish oil caps; they have all the things you need at prices the grocery stores can’t touch.