Cooking method:

1. Preheat the oven to 180°C/350°F/Gas 4.
2. Unwrap lamb and slash meat 20-30 times with a sharp knife. Poke small sprigs of rosemary into the lamb, place in a roasting tin and dribble with 1 tbsp of the oil. Season with salt and pepper.
3. Cover loosely with foil and roast for 1 hour 30 minutes.
4. Increase oven temperature to 220°C/425°F/Gas 7.
5. Toss all the vegetables with the remaining oil. Remove lamb from oven and discard foil. Scatter vegetables around the lamb and roast for 35-45 minutes until the lamb is cooked and the vegetables are tender and lightly charred.
6. Turn the vegetables once during cooking to ensure even browning.
7. Place lamb and vegetables on a serving plate. Cover loosely with foil and leave to rest in a warm place. Spoon off as much fat as possible from the roasting tin.
8. Place tin on the hob and add the water or lamb stock. Bring to the boil, stirring to scrape up the pan juices. Simmer for 1-2 minutes and season to taste.
9. Carve lamb and serve with vegetables and a little pan gravy.