Grate zest of the lemon in a bowl. Add salt, pepper, mixed herbs, rosemary and mix well. Set aside.
Wash, clean and pat the chicken dry (very drwith paper towels all over, including the cavity. Rub the seasoning mixture over the chicken and inside the cavity. With fingertips, gently separate the skin from the meat of the chicken breast and push some seasoning mixture under the skin. Leave the chicken to marinate for at least 4 hours or up to 24 hours.
Remove chicken from fridge and let it rest in room temperature for at least 30 mins so that it will cook evenly. Brush melted butter (or olive oiall over the chicken.
Peel and cut the potatoes into halves or quarters. Put them into a pot of water with a pinch of salt together with the whole lemon. Bring to a boil and continue to cook for about 10 minutes. Drain and allow to steam dry for 1 minute. Return the potatoes to the same pot. Toss the potatoes with some salt, freshly grounded black pepper and a little olive oil. Do this while the potatoes are still hot so their outsides get chuffed up and fluffy.
While the lemon is still hot, carefully pierce it with the tip of a sharp knife about 10 times. Stuff the lemon inside the cavity of the chicken.
Put the potatoes in a roasting pan. Tuck the wings underneath the chicken and place it breast side up, on the potatoes. Cook in preheated oven at 200º C for around 40 - 45 minutes or until the skin is nicely browned. Turn the chicken over and roast for a further 30 minutes or until the skin is browned. Turn the chicken breast side up again and roast for another 10 - 15 mins until the chicken is done and the potatoes are nice and golden. To test whether the chicken is done, pierce the tip of a knife near the joint between the drumstick and the thigh. The juices should run clear (not pink), if it is still pink, cook the chicken a little longer. Carefully remove the lemon from the cavity. Let the chicken rest for 10 minutes before serving. This allows the juices to settle and the chicken will be much more succulent.