Make sure you have a good-sized roasting tin to fit the goose and a grid to place under it. Preheat the oven 425 degrees F. You can make the stuffing in advance.
Soak the prunes in hot tea (Earl Grey) until soft, stone them and drain, or get pre-stoned ones - easier. Place prunes, vermouth and stock in a saucepan, bring to the boil, then simmer for ten minutes until tender. Strain but reserve the liquid.
Melt the butter in a little pan and gently fry the shallots and liver for a couple of minutes, stirring all the while. Place in a mixing-bowl which will hold all the ingredients. Boil the port in the same pan until reduced to two tablespoons, scrape round the sides and add to the liver mixture. Beat the pate, bread crumbs, allspice and thyme together and combine thoroughly with the rest. Season with salt and a good quantity of the pepper. Stir in the prunes.
Put the goose in the sink and pour a kettle of boiling water over it. This ensures a good, crisp skin. Remove and dry with kitchen towels. Salt the cavity and fill loosely with the stuffing, then sew up the vent. Prick the skin all over but not the flesh. Place on the grid in the roasting pan and roast breastside up for 15 minutes.
Lower heat to 350 degrees F, turn the goose onto its side. Halfway through, turn onto the other side, then for the last 15 minutes onto its back again. Throughout the cooking, baste every 20 minutes with three tablespoons of boiling water and remove the fat from the pan into a bowl. The easiest way to perform both these operations is with a bulb baster. The whole cooking time should be 2 1/2 hours. Test by piercing the thickest part of the thigh: the juices should run pale yellow.
When ready, the goose should be put on a very hot dish. Pour off the remaining fat from the roasting pan and make the gravy from the reserved prune liquid, adding it to the residual juices in the pan. Bring to the boil and simmer for a few minutes, adjust the seasoning, strain into a sauce boat and hand round separately.