What you should have done is not left it until now to lose weight and started months ago. With a moderate deficit you could lose that easily over a few months. Also these diets you're talking about aren't sustainable and you will just gain the weight back when you stop it, you're losing water not fat. Work out how many calories you need to eat each day to keep the same weight, then eat ~500 less.
NB: I'm not saying that if you lose weight you will gain it back.
As I have said, I am not worried if it get's put on very soon after, as I need to loose as much as I can for just one particular day even if it's water loss.
So you are saying you can have a few months of an unhealthy lifestyle and gain two stone but want to lose it in only a week? World doesn't work that way
If I asked on here I want a high paying job in finance but can't be bothered with a 3 year degree-can I do it in 1 semester? I would be branded a lazy fool. Same applies here as harsh as it sounds-my first impression is that this is someone who is just too lazy and wants a quick fix solution. "Lose it even for a day, even if it is water loss". Yeah-looks matter to you more than your health evidently. Harsh but true.
Why don't you try and make more of a lifestyle change than trying to shed a probably impossible amount of weight in that time frame - look at clean eating and aim to get your heart rate up once a day, if only for twenty or so minutes - everyone can find twenty minutes in their day
Losing that amount of weight that quickly is not healthy and it certainly won't stay off permanently.