If using gages or damsons add to a pan with half the vinegar and stew gently for 20 minutes, wait for the mixture to cool and then remove the stones by hand or using a slotted spoon. If using plums halve and roughly chop them.
Once the stones have been removed add all the ingredients apart from the sugar to the pan, slowly bring to the boil and then cover and simmer for 10 minutes.
Stir in the sugar plus 2 tsp salt and keep stirring until it has dissolved. Boil the chutney for 20-30 mins, uncovered, stirring occasionally to prevent it catching on the bottom, until it is thick and pulpy.
Pot into sterilised jars, seal, label and store for at least 2 weeks before eating. Will keep for up to 6 months in a cool dark place.