Heat the oil in a roasting tin in which the lamb will fit snugly. Add the lamb and cook until browned all over. Leave to cool.
Pound 6 of the juniper berries, the garlic, anchovies and chopped rosemary with the end of a rolling pin in a bowl. Stir in the vinegar and mix to a paste. Make small incisions all over the lamb with a small, sharp knife. Spread the paste over the lamb, working it into the incisions. Season with salt and pepper. Put the rosemary sprigs in the roasting tin and put the lamb on top. Pour in the wine and add the remaining juniper berries.
Cover the roasting tin with foil and bring to the boil, then cook in a preheated oven, 160°C (325°F), Gas Mark 3, for 1 hour, turning the lamb every 20 minutes. Raise the temperature to 200°C (400°F), Gas Mark 6, uncover and roast for a further 30 minutes until the lamb is very tender.