Yep - I've done it!
I was 19 stone at 5' 3" and decided it was time to do something about it, having gone from a size 10-12 at 18 to a 20 by age 20, then steadily creeping up over the years.
I went to see my Practice Nurse and she weighed me and suggested a target calorie amount and I then had a weekly 'weigh in' appointment with her where she also offered advice and support, which helped me to stick to the diet as I knew she would be aware if I wasn't.
My best tip is to write everything that you eat down, along with the calorie content and to be totally honest with yourself about it - I'd even include things like 'a bite of DD's fishfinger', or 'one square of chocolate'. It was quite time consuming initially, but you quickly get the hang of it.
Once I had lost a couple of stone and felt more confident, I was weighed monthly instead of weekly, but my Practice Nurse was always able to offer me support and advice if I needed it. About 6 months in, I joined the gym and did a bit of everything, to try and tone up to try to help with the loose skin - it was worth it; my stomach is a write off (but I have had two big babies so I was never likely to feel comfortable in a bikini), but I'm happy to have my arms on show.
It took me nearly 2 years to get to my target of 9 stone, but I then became very poorly (unrelated to dieting) and lost a further 2 stone and looked (and felt) horrific. It was quite a mental battle to get into the right frame of mind to gain weight after dieting for so long. I now hover between 8st 12lbs and 9st 2lbs and I just weigh myself once a week. My appetite is loads smaller than it was when I was big and I don't get the sugar cravings I used to have, so it's easier to stop eating when I'm full and to say no to puddings.
It can definitely be done, it's like any addiction, you have to be ready to do it yourself, no one else can tell you. I wish you loads of luck and tons of will power!