Prick each sloe with a fork and drop them into a clean, dry 1 litre (1¾ pint) wide-necked, screw-topped bottle.
Using a plastic funnel or a cone of paper, pour the sugar into the bottle. Stick the cloves into the orange rind and add to the bottle along with the halved cinnamon stick.
Pour in the gin, seal with an airtight top and turn the bottle upside down 2–3 times.
Stand the bottle in a cool place and turn it once a day for 7 days until the sugar has completely dissolved.
Label the bottle and leave to mature in a cool, dark place for 6 months or longer if you can (the longer you leave it the mellower and more delicious it will be). The sloes should be discarded before the gin is served.