Put all the ingredients into a large pan and heat gently until the sugar has dissolved.
Bring to a boil and skim off any scum that rises to the surface. Reduce the heat and simmer gently for 45-50 minutes until thick, stirring occasionally.
Continue cooking for a further 10-15 minutes, stirring frequently, until very thick. Remove from the heat and cool slightly.
Spoon into hot sterilised jars, cover, seal and label.