It depends what weight you are to start off with. If you have several stones of excess fat, an abrupt change like that can allow you to shed it fairly quickly. If it more a case of sliming right down/toning, it can be harder and take longer.
This sounds a fairly harsh regime, to be honest. Do you have something in particular that you're trying to lose weight for (i.e. a time limit?) If you want to keep weight off in the long-term, you need to make your diet/exercise something that you can live with. The risk otherwise is that you'll lose weight for a while, then put it straight back if you stop exercising/dieting.