If you have then you will know it is calorie based, the calories they have advised me to have are quite high (1650ish to lose 1lb a week) and this worries me.
Has anyone lost weight on this plan?
Thanks xx

I have not tried the plan, but 1650 calories is not high. The daily recommended allowance is between 2000 and 2500 depending on certain factors.
If you eat too few calories, your body will think it is starving and start storing fat, which is the last thing you want when trying to lose weight.
Eat the 1650 and do some light exercising, and the lbs will start coming off. Even if you're just walking for 20-30 minutes 3x a week, it will help.