2 stone in 4 weeks?? Well that equates to one pound a day.
If you do not want to dehydrate yourself or have your metalbolism cut in to your protein (muscle), then it will only be possible through rigorous areobic exercise.
That is 3500 extra calories a day you need to burn off. That is about a half marathon a day for 28 days.
Can be done, but quite tough for somebody who is two stone overweight.
Also the skin will not shrink back in time due to this rapid weight loss and you may be left with saggy bits everywhere.
I once lost three stones in about 2 weeks on a jungle training exercise. I do not know how much was water, and I was very dehydrated at the end. We also ate like kings, but as we were probably each buring 12-15000 calories a day, you just couldn't keep up with calorie intake, no matter how much food was available.
My advice, unless you are a supreme athlete with a strong heart, you shouldn't lose more than 5 pounds a week. Most medics say 2-3 pound a week continually is safe.