Add boiling water to jelly crystals and stir until all the crystals have dissolved then set aside to cool. If you try adding cream at this point it may curdle, so always leave the jelly to cool first
**NOTE, do not add additional cold water as directed on the packet
Once cooled to room temp pour in the cream and mix to blend well
Pour the mixture into ramekins or glasses and leave in the fridge to set for at least 2 hours or until set
To make more of a trifle, add a thin layer of the jelly to each glass and refrigerate to set, then add the remainder of the double cream to the leftover jelly to create the fluff mixture and pour on top of the set jellies. Refrigerate again so that the fluff sets on top of the layer of jelly. You could also add some more whipped cream and a shaving of chocolate or chopped nuts for a topping!
The other option is to use full fat yoghurt instead of cream.