Preheat the oven to 180ºC, fan 160ºC, gas 4. In a small bowl, mix together the butter, garlic, pepper & chilli seasoning, tomato paste and the leaves from 4 sprigs of thyme.
Put the chicken into a large roasting tin and, using clean hands, rub the butter mixture all over the skin. Stuff half of the remaining thyme into the chicken cavity – remember to wash your hands afterwards.
Add the potatoes, parsnips and peppers to the tin. Drizzle the oil and the remaining thyme sprigs over the veg, and scatter the chopped chilli over the chicken.
Roast in the oven for 1 hour 45 minutes until cooked – the juices should run clear when a skewer is inserted into the thickest part of the thigh. Cover the chicken with foil halfway through cooking to prevent the butter from burning.
Remove from the oven and set aside for 15 minutes – keep the tin covered with foil so the veg stays warm. Carve the chicken and serve 120g per person with the roasted vegetables.