For all those of you who are experiencing the horror of significant weight gain after cheating, perhaps I can reassure you a bit?
What you do when you cheat is to re-stock your glycogen stores; and the glucose stored in there is bound up with water, so it adds a lot of weight - but this isn't fat!
Drink more water, be extra strict with the low carbing, and considering upping your exercise or doing some (if you don't already) to use up that stored glycogen. It's stored for your body's future energy needs, so use up a bit more energy now!
Above all though, you're beginning to see that you can't just dive into the cakes and biscuits without seeing consequences.
I'm sorry to have to break this news to you 
Of course, what this means is that in the future, once you've achieved your target, this will also happen in real life. So it's not to say that you can never have cake or biscuits (or whatever your preferred treats are), but that you will see your weight go up - in the short term - as a consequence.
This is why StuntNun talks about setting a limit that's above your maintenance weight. When you reach that magic number, your body will quite naturally fluctuate - as well show increases if you increase your carbs too much. It means you need to be vigilant; if you know you've over-eaten on the carb front, then cut back for the next few days until things return to 'normal'.