Open the tin of fruit and strain the juice or syrup into a cup. Make up 1/2 pint (2 cupfuls) of the fruit juice by adding water if necessary. Heat the juice and water in a saucepan, until it is just boiling. Remove from the heat and add the jelly. Stir until the jelly melts. Leave a few minutes to cool, then put into the fridge, freezer, or other cold place, until the jelly is half-set. (This will take about 1/2 to 1 hour according to the temperature: the colder it is, the quicker the jelly will set).
When the jelly is half-set, arrange the fruit in the sponge flan in pretty patterns. Spoon the half-set jelly on the top and leave in a cool place to set completely (15-30 minutes, depending on the temperature). Leave any spare jelly to set, then mash with a fork and serve separately with any spare fruit. (If the jelly gets too set before you remember to finish the flan, it can be thinned down by carefully adding 1 to 2 tbsp boiling water to the set jelly and stirring hard, to make it soft again).