Stone the cherries and place the stones in a large saucepan. Peel, core and thickly slice the cooking apples, then sprinkle the slices with the lemon juice and set them aside.

Add the apple trimmings to the pan with the cherry stones and pour in the water. Bring to the boil and cook, uncovered, until the liquid is reduced to about one third of its original quantity. This will take about 1 hour.

Press the resulting pulp through a fine sieve and return it to the rinsed-out saucepan. Add the prepared cherries and apples and bring the mixture to the boil.

Cover the pan and simmer gently, stirring occasionally, for 10 to 15 minutes, until the fruit is soft.

Pour in the sugar and heat gently, stirring, until the sugar has dissolved. Bring the jam to a rapid boil and boil hard to setting point.

Stir in the butter to disperse any scum and pot the jam into warmed jars. Cover the surfaces with waxed paper discs, waxed sides down, and allow to cool.

Top the pots with cellophane covers or lids and label them when cold.