In a small saucepan, bring the stock to the boil over moderate heat. Remove from the heat and stir in the prunes and apricots. Leave to soak for at least 15 minutes or until very soft.
Meanwhile, preheat the oven to 160 degrees C. Trim all the fat from the pork loin, then open it out and pat dry with a paper towel. Season the inside with pepper.
Drain the soaked fruit, reserving the liquid in the saucepan. Place the fruit along one of the long sides of the pork loin. Scatter the diced garlic and thyme over the fruit.
Fold the long edge of meat over the fruit and roll up the loin. With kitchen string, tie at regular intervals to seal in the stuffing.
Place the loin, seam side down, on a rack in a roasting pan. Roast for about 30 minutes. Meanwhile, add the Madeira or port wine, if using, and molasses to the reserved soaking liquid and bring to the boil to make the glaze.
Brush the glaze evenly over the pork loin. Roast for a further hour or until tender and juices run clear. Brush with the glaze every 10 minutes during the hour of cooking.