When I embarked on the Newcastle Diet(ND) I used the official recommendations of 3sachets of Optifast soup, 2cups of raw or steamed vegetables per day and 1 teaspoon of olive oil. As well, I drank up to 2 litres of water. The trial lasted for 8 weeks originally, but then was continued for another 4.
However, there is a school of thought which maintains that the same benefits will ensue by eating a diet restricted to 800 calories, drinking plenty of water, and a spoonful of oil ( this is to be protective of the gall bladder, I believe). In this case, it would seem possible to eat the sugar free jelly and the diet drinks, but you would have to be careful that ,as well as keeping within the 800 calorie limit, you were also maintaining nutrient levels.
Many people have "done" the ND, on this forum, some more than once. I am sure others will respond soon.
If you Google Newcastle Diet, there will be useful information. Hope this helps. Good luck.