Mix everything apart from the chicken together in a large saucepan big enough to hold the chicken. Place over a medium heat and bring to the boil. Stir until the sugar and salt has dissolved. Remove from the heat and allow to cool completely.
Prick the chicken all over with a skewer and submerge in the brine. Cover and place in the fridge overnight.
The next day, remove, dry the chicken with kitchen paper, place on a plate and into the fridge for at least an hour to dry out.
Follow your favourite roast chicken recipe, but keep an eye on the colour as the brine can make the chicken brown faster.