Dice the pumpkin, then add to a preserving pan with all the remaining ingredients. Cover and cook gently for 1 hour, stirring from time to time, until softened. Remove the lid and cook for ½–1 hour, stirring more frequently towards the end of cooking as the chutney thickens.
Ladle into warm, dry jars, filling to the very top and pressing down well. Disperse any air pockets with a skewer or small knife and cover with screw-top lids. Label and leave to mature in a cool, dark place for at least 3 weeks.