The Cambridge diet is a plan where you can replace part or all of your three meals a day with food packs consisting of shakes, soups and bars.
At the 'strictest' end, it's called Sole Source (SS) because you replace all three meals and it's the sole source of your nutrition.
It works by putting your body into a mild state of ketosis ... that is, so few carbs that your body uses its own fat stores for energy.
Consequently you lose weight quickly and the averag loss is a stone per month.
Is it good? Once you've overcome the first week (pretty hard) and are in ketosis, it's quite easy because you don't experience hunger ... you do have to combat psychological hunger (I want food ... not 'I'm hungry')
As for weight gain after you stop ... if you return to the habits you had BEFORE the diet then you're likely to regain weight - but that's true of ANY diet.
I think you have to be quite desperate and very determined to go along the SS route - although there are other CD plans to suit circumstances.
To answer your last couple of questions, you are statistically less likely to put the weight back on again with CD as you go through maintainance plans..
Is it hard? I haven't found it hard AT ALL, I have no urge to cheat (unlike WW, now that WAS a daily battle!) and I'm loving the weight loss.. I think that in itself spurs you on hugely!!! I dont do SS, I started on the 1000 plan and it's worked enough for me!!!
Prices vary because CDCs are self-employed and can charge whatever they like ...
However, MOST tend to base the price around the average of about £32 per week for SS (three packs per day). That may sound a lot but when you consider that you don't need to buy ANYTHING else, it works out to be very reasonable (around £1.55 per meal).
There are nine flavours of shake, four soups and five bars (I think). I think the shakes are lovely - although obviously you develop your own preferences.