Right (sorry to be so nosey
), that makes a difference - if you were stressing about being 8 stone instead of wanting to be 7, then the advice would be very different!
You say you're crap at diets - what do you mean? I think most of us are pretty crap at diets (just look at any of the threads here and you'll get my drift!), and it's most often because you feel deprived, or you start something too punitive and try to do too much/expect too much too soon.
From my experience, if you're wanting to shift a substantial amount of weight in a short period of time, without feeling deprived, then a low carb diet is definitely the way to go. They key thing about LC is that you eat a lot more food than you would expect, so you are less likely to feel deprived - you won't be hungry for a start. None of those gnawing pangs at around 11.00, meaning that you end up reaching for the biscuits!
Lots of people can lose easily 7-10lbs in the first two weeks, especially if they are larger to start with. In weeks 3-5 weight loss will slow, possibly stop, but thereafter will continue at the more usual 1-2lbs per week.
The only real issue is that, to do it properly, you need to take a phased approach, so that you gradually re-introduce (some) carbs back into your diet. If you go from extreme low carbing back to your normal diet, you will suddenly pile 4-5lbs back on, which you won't be wanting to do!
The best book I can recommend you to read is India Knight/Neris Thomas's The Idiot Proof Diet (and get the recipe book that goes with it too). It has three phases. The first phase lasts for 14 days, and is the most strict (although you will still be able to eat lovely food that means you will not feel that you're on a diet!). The book gives you a day-by-day 'guide' - and it talks about your psychological motivation as well as more practical stuff.
HTH - and good luck!