As said above, small cereal plus limited milk and sugar, or cereal and fruit (like blueberries), no lunch and a non carbohydrate meal in evening, like chicken. Sainsburys do stuff like stirfry veg and a sauce tht, with chicken, can keep you within the daily allowance. There's probably loads of...
Stay below 600 calories on two non consecutive days two days a week and eat NORMALLY for the other 5 days. It's called Intermittant fasting and it works.