Immerse the gelatine leaves one at a time in a shallow bowl of cold water and leave for a minute or so until soft.
Bring 100ml/3½fl oz of the Perry to the boil in a medium saucepan, add the sugar and stir until dissolved. Drain and squeeze the gelatine leaves, then add to the hot Perry and stir until melted. Remove from the heat, add the rest of the Perry and stir well. Put the pan of jelly somewhere cool, but do not let it set.
Divide half the berries among four individual jelly moulds, or use one large mould. Pour in half of the cooled jelly. Chill for an hour or so to set, then top up with the rest of the berries and unset jelly. (This ensures the berries stay suspended and don't float to the top.) Return to the fridge to chill until set.
To serve, turn the jellies out onto plates and place a scoop of ice cream.