Preheat the oven to 200°C. Place all the ingredients, except the chicken, in a small bowl and stir until mixed.
Place the chicken in a roasting tin. Loosen the skin around the breast by sliding your fingers between the skin and the meat. Push a couple of dessert spoonfuls of the BBQ sauce between the skin and the meat, gently easing it under the skin so that it covers both breasts.
Reserve 2 tbsp of the BBQ sauce and spread the rest over the whole chicken. Cover with a large sheet of kitchen foil to make a 'tent', so that the foil isn't touching the chicken. Seal tightly around the edges.
Place the covered chicken in the preheated oven for 1 hour. Remove the kitchen foil and spread the remaining BBQ sauce over the chicken.
Leave uncovered and return to the oven for 20 minutes, until the chicken is thoroughly cooked through, and the skin has a crusty BBQ coating. Check that it's thoroughly cooked by inserting a sharp knife into the thickest part of the leg. The juices should run clear and there should be no sign of pinkness.
Serve with Butternut Squash Roasties and Garlic Green Beans or other accompaniments of choice.