does the cornflake diet really work?

[mustsleep]

just that really want to lose a stone and don;t mind cereal and think i am less likely to feel hungry if i get to eat it twice a day

is there anything else you are supposed to do whilst on it?

Well ... it will work in the short term because it limits the amount of calories you're taking in. It's not a terribly well-balanced eating plan though, and it won't make you less hungry than having two sensible, calorie-controlled meals would.