

Beat all the marinade ingredients in a large bowl for four minutes. Put the lamb on a board and season well. Rub the lamb all over with the yoghurt marinade - really work into both sides.
Put it in a freezer bag with any remaining yoghurt marinade and refrigerate for up to 12 hours.
Pre-heat the oven to 180C/350F/Gas 4 and heat the olive oil in a roasting tray. Seal the lamb and roast in the oven for up to 2.5hours, depending on how you like your meat cooked. Leave to stand before carving to allow the juices to soak in. Serve with roast potatoes.