Bash the coriander seeds in a mortar and tip into a bowl; add the grated carrots, ginger, sugar and zests, and put into the fridge to macerate for at least two hours to draw out the liquid.
When the carrots are done, mix the honey, citrus juices and vinegar with half a teaspoon of salt in a large heavy-based pan, and stir until the salt has dissolved.
Tip in the carrot mixture and slowly bring to a boil, then reduce the heat and simmer for 15 minutes, until the carrots and ginger are tender.
Turn the heat up and boil until almost all the liquid has evaporated. You will need to stir it towards the end to make sure it doesn’t stick.Spoon into warm sterilised jars.