Beef rib roast with roast potatoes

1) Preheat the oven to 220C/425F/Gas 7.
2) Boil the potatoes in a large pan of salted water until just soft. Drain in a colander and shake so that the edges fluff up.
3) Score the beef all over with a sharp knife.
4) In a saucepan, melt 250g of the dripping with horseradish, salt and pepper.
5) Layer the carrots and parsnips in a large oven tray and place the beef on top. Pour the horseradish glaze over the top of the meat.
6) Roast in the oven for 20 minutes then reduce the temperature to 160C/325F/Gas 3 and baste the meat with the dripping in the bottom of the tray
7) Melt the rest of the dripping in another tray and when sizzling add the potatoes. Baste with the dripping then place in the oven to cook for the rest of the beef cooking time.
8) Roast the meat for two hours, basting it with the dripping every half hour.
9) Remove meat from oven and allow to rest under foil for 30 minutes before serving.
10) While the meat is resting, baste the potatoes and turn up the oven to crisp the potatoes.