Hi Amelia,
I've been using the Tesco shakes diet for about two years now. I was always one of those who scoffed at the idea of these sort of 'shake' diets, until I tried it myself. I went on it because I needed to loose weight before having a gastric bypass op (which I never had). I lost about two stone on the diet but then went through depression and gave up. I'm back on it again now and I swear by it.
Initially all I was having was a shake for breakfast, one for lunch and a weight watchers or lighter choices ready meal in the evening, but that made me ill as I have blood sugar issues, so I introduced snacks into it on the advice of the dietitian.
Now I have a shake for breakfast, a banana mid morning, shake for lunch, grapes or some sugar free jelly mid afternoon, an evening meal and I sometimes have another 100 cal snack if I feel peckish. I also try to interspace each food intake with a cup of tea (no sugar and just a little skimmed milk), as that fills my stomach. That way, almost every hour or hour and a half, I am having some kind of intake, and if I feel hungry, I just remind myself that I only have 20 mins to go before my next 'fix' and go off to do something to pass the time so that I don't pig out then feel empty later - believe me, it works!
I also found that delaying my breakfast shake helped bypass a couple of hours, as I am not usually that hungry first thing. As I tend to get up at 6am, if I started my intakes then, I'd have bigger gaps between intakes throughout the day. As I don't feel hungry in the mornings, I leave my breakfast shake until I get back from the school run and have put some washing on or cleared up a bit, by then I am feeling like I need something, so then I have my first shake.
May not work for everyone, but it works for me. I also set myself little targets such as half a stone at a time, it makes it much easier. I also don't buy sweets and biscuits etc when we go shopping.
I did read somewhere, (it could even have been on the shake box itself), that you can have a third shake during the day if you find that more filling than say snacks etc. Sugar free jelly is good, and I eat it with a tiny spoon as it seems more that way.
One thing to consider, is that you may not be loosing weight initially depending on your monthly cycle. I always put on a pound or two when I'm due on.
Hope that helps.