Tanny, I lost almost 10, it took around about 2-3 years. I still have 4 stone to go. Started at 23 stone, am at around 14 and a half at the moment. Stalled a bit this year, but I find I get the 2 year diet itch. It's coming up to my second one. The last one was at 18 stone, stayed at 18 stone for about 8 months and then kickstarted myself again.
You'll get there mate, but I would say don't give yourself a time frame. I learned this from my years of 'Oh, i'm not going to make it so I may as well stop trying'.
I keep trying but at the moment I'm struggling. Have 7 weeks to get back into a dress that fitted just before Christmas. A good stone off should do it, but if I don't make it in 7 weeks, am going to see it as a good excuse to rummage around the sales!