You can either reduce the calories in - so that's tackling the "large portions of unhealthy food with evening comfort eating of crisps, chocolate and ice-cream", or you can do about 4000-5000 cals of exercise a day.
Now, I'm actually a fan of this - as a short person who likes cake, the only way I can realistically chomp through 2000 cals a day is to take up cycling, long walks and powerlifting. Voila, balance is achieved and I can eat pie.
However, that's the realm of the 2000s.
Large portions, plus the extras are going to be stacking up to thousands more, far more than even a massive male powerlifter could burn off.
So the focus has to be on the behaviour. Ensure the food isn't in the house and then just, well, willpower really. Distract. Fill up on greek yoghurt (normal, not low-fat, and not STYLE either, proper stuff). Nibble a salty rice cake. Plan some protein-rich meals with smaller portions of carb and larger of veg. Yes it's hard for the first few days but it becomes habit, just as comfort eating became a habit.
You don't need 'a diet'. It's like if you were bopping yourself in the face with a hammer every day, a carefully managed but complicated plan about the sort of hammer you use and the angle you bop your face is all well and good, and might even be a bit better for a short time, but it didn't really tackle the core issue which is you're bopping yourself in the face with a hammer. So that's the bit that needs tackling. Putting down the hammer :)
Also I totally recommend powerlifting, dead good fun.