What is different here is that you dont preheat the oven: a very handy method for when you are in a hurry (or just plain forgetful) which also produces a golden-skinned bird.
1. Smear the butter over the chicken, place it in a roasting dish that holds it snugly, pour over the lemon juice and pop the squeezed-out lemon halves inside the cavity. Season and place in the cold oven.
2. Turn the oven to 220C/200C fan/425F/gas 7 and roast the chicken for 1 hour (about 10 minutes longer than the usual roasting time), basting halfway through.
3. Rest out of the oven for 15 minutes, then carve and serve with the warmed roasting juices spooned over.