Soak the gammon rashers in cold water for 2 hours to draw out surplus salt. Drain and pat dry. Trim off the rind and rub a little oil over the lean meat. Place under a hot grill for about 2 minutes each side to seal. Then reduce the heat and cook gently for 4 minutes on each side.
Meanwhile put the raisins in a saucepan with the cider. Add the sugar and salt and stir in the cornflour which has been blended with the water. Stir until boiling, then cook for a few minutes until the sauce clears and thickens slightly. Add the vinegar and butter, stir until blended and then serve with the gammon.