Hi Louise/Lucy !
Welcome to SW. I am sure that it is possible but it is a pretty tough challenge. I have lost almost 3 and a half stone in just over 4 months. I have had quite a few meals out during that time and a holiday but I stick to plan the vast majority of time.
For me, I wouldn't want to set myself such a tough challenge because I wouldn't want to risk feeling disheartened if you did really well but not 'well enough' eg lost 4 stones in 8 months and then fall off the rails. However if you think you'd respond well to the challenge and be happy no matter what you achieved then go for it. Remember, this is not a race - the idea of SW is that it is a plan for life. For most of us the weight didn't go on overnight, nor the eating habits that went with it, so it is unlikely to come off straight away either.
You will get plenty of support here as well as advice and friendship. Sorry to be so negative - I'm not usually but I really would like you (and everyone else here) to succeed (which I am sure that you can - if I can, anyone can !). So I hope you find the right way to do this and best of luck. Keep posting and hope to see you around.
Gail x