Prepare the jelly: Make the jelly according to the packet instructions and let it set in the fridge until firm.
Layer the Swiss roll: Arrange slices of Swiss roll at the bottom of a large glass bowl. Sprinkle lightly with sherry if using.
Add the fruit: Spoon over the drained fruit cocktail evenly.
Jelly layer: Cut the set jelly into cubes and scatter over the fruit.
Custard layer: Pour custard on top, spreading it evenly.
Whipped cream: Finish with a thick layer of whipped cream.
Decorate: Sprinkle flaked almonds, grated chocolate, or place a few cherries on top for a festive touch.