Add the peaches to a preserving pan with the lemon rind and juice and measurement water. Cover and cook gently for 15 minutes, until the peaches are just softened.
Add the raspberries with the sugar and cook gently, stirring from time to time, until the sugar has dissolved. Bring to the boil, then boil rapidly until setting point is reached (5–10 minutes). Skim with a draining spoon or stir in butter if needed.
Ladle into warm, dry jars, filling to the very top. Cover with screw-top lids, or with waxed discs and cellophane tops secured with elastic bands. Label and leave to cool.
To serve, this conserve goes well with vanilla ice cream and sliced peaches.