Prepare the sugar syrup first, before preparing the fruit. Measure the water into a saucepan, add the sugar and stir over low heat until the sugar has dissolved. Bring up to the boil, simmer for 2 minutes and draw off the heat.
Wash the plums, remove the stalks, then halve the fruit and remove the stones. Wash the grapes and remove any stalks – halve and deseed if using large grapes. Plunge the peaches into boiling water for 30 seconds, drain and place in cold water. Peel away the skins, halve the fruit and remove the stones. Keep submerged in cold water until required. Halve, core, quarter and peel the pears and keep submerged in cold water to prevent discolouration.
Pack a selection of the fruit in each of six clean jars. Stand the jars about 5 cm (2 in) apart on a baking tray lined with folded newspaper. Bring the syrup up to the boil and fill each jar to the brim with the hot syrup. Cover with the lids or rubber rings and lids, according to the type used. Place in the centre of a slow oven (150 °C., 300 °F., Gas Mark 2) and process for 1 hour 10 minutes. Remove the jars from the oven; using an oven cloth to protect the fingers press down the lid on each one and seal or put on the screw caps and screw down tightly. Leave until quite cold. Test the seal before storing.