Thanks again for the responses.
maddening - This is how we did gradual retreat. I'm sure others have been different, as it took us AGES, but I couldn't hack leaving her to cry. First a bit of background.
She used to settle OK in a cot in our room until she was 10 months, but was still waking a few times a night for milk or water. Then we moved house and tried her in her own room (thinking back we probably should have done that in stages, but I didn't know any better). She completely freaked and refused to settle AT ALL. We ended up having to settle her in our bed, with me lying there and then leaving once she was asleep. Due to the size of our bed DH had to sleep downstairs. This went on for about 5 months until I decided enough was enough and she was going back in her cot. I missed DH being there to be blunt.
The first step was taking the side off the cot and pushing it up against the bed. To start with I would still lay there until she went to sleep. We did this for a couple of weeks and then the side went back on the cot and the cot went away from the bed. I would sit on the bed until she went to sleep. Another couple of weeks and I then sat on the other side of the bed (so further away). Once she was used to that we put the cot back in her room and I would sit in a chair. We stayed at this stage for a few weeks, sometimes it would take her two hours to go to sleep 
I know we probably could have done this quicker, and I'm sure many do, I'm just relaying exactly how it went.
Then one day I just left the room and stayed outside. She cried, and I would go in to her every couple of minutes just to let her know I was there (I suppose this is a variation of controlled crying, but I didn't know what else to do). It took about an hour the first night I think. It then got to the point where I could just leave the room. She was still waking in the night sometimes and sometimes she was still coming in the bed in the early hours - it was just easier than either listening to her cry or settling her back down in her cot.
Now she doesn't often wake in the night, but occasionally she does. Some nights she just will not settle in her cot and so we still co-sleep - maybe one or two nights a month. It is SO much better now, and I can't believe it took us so long to sort out.
So basically (sorry for mahoosive post) if you're thinking of doing gradual retreat, I would break it down in stages. In cot next to bed, away from bed, in her/his room but with you close, and then move away. How long you do each stage for is completely up to you and how you feel comfortable. I hope that helps 