Begin by making the jelly. In a pan, pour in the orange juice and add the sachet of vege-gel. Whisk gently until dissolved. Heat the mixture to boiling point then remove from the heat. Add the lemonade and stir. Pour this into your trifle dish and refrigerate. Vege-gel sets quickly.
Break the chocolate into a microwaveable bowl and microwave for 1 minute, stir, and return for 30 seconds, then for 10 second intervals stirring in between until melted, be careful as it can easily burn.
Heat the custard in a pan then add the chocolate and stir to combine. Transfer to a bowl and leave to cool in the refrigerator.
In a pan, gently heat the marmalade with a splash of the mandarin juice and whisk to loosen. Take off the heat and leave to cool.
In a bowl, whip 900ml of the cream with 60g icing sugar and 2 tsp of vanilla extract until soft peaks. Refrigerate until needed.
Slice 1 swiss roll into 8 pieces and the other half into 4 pieces. Line the pieces facing out around the trifle dish on top of the set jelly. Use the rest of the pieces to make a base in the middle on top of the jelly.
Fill the middle of the sponges with whipped cream and top with the mandarin pieces, then add more whipped cream making a layer above the swiss rolls.
Add the custard on top of the cream, gently spread to the edges.
Add more cream on top of the custard. For a neater look, use a piping bag then gently smooth with a spatula. Leave enough room at the top of the trifle for the marmalade.
Pour the marmalade on top, gently spreading to the edges. Chill the trifle in the refrigerator.
Whip the rest of the cream, icing sugar and vanilla until firm enough to pipe, being careful not to over whip. Using a star nozzle, fill a piping bag with the cream and pipe swirls on top of the trifle.
Slice 2 oranges and arrange on top. Sprinkle with the zest of the other orange.