Put all the ingredients in a preserving pan over a medium heat. Slowly bring the mixture up to a simmer, stirring regularly until the sugar has dissolved.
Reduce the heat and gently simmer the chutney for 1½–2 hours, stirring every so often to stop it sticking to the base of the pan. The chutney will thicken as it cooks; you’ll know it’s ready when you can draw a wooden spoon across the bottom of the pan and it leaves a path behind it for a few seconds before the chutney collapses back down and covers the base. Be extra-careful it doesn’t catch and burn at this point.
Remove the chutney from the heat and spoon carefully into jars, still warm from sterilising. Seal with the lids and cool. Store in a cool, dark place for several months before eating – although you can eat it earlier, if you like. Once open, store in the fridge and use within a month.