Put the Swiss roll chunks in a bowl. Divide the cake between 6 x 200ml (1/3pt) tumblers or dessert glasses. Top each with a layer of the fruit. Set aside until needed.
Put the jelly in a measuring jug and pour over 185ml (6 1/2fl oz) just-boiled water; stir until dissolved. Add 50ml (2fl oz) water and the clementine juice.
Pour the liquid jelly mixture over the fruit and cake, to come two-thirds of the way up the glasses. Chill for 3-4 hours, until set. Spoon the custard over the set jellies. Chill for at least 1 hour, or until just before serving.
Combine the cream and orange zest in a bowl and whip to medium - soft peaks. Top each trifle with a spoonful of the cream, then decorate with the chocolate shavings.