Preheat oven to Gas Mark 4, 180°C, 350°F.
Cut liver into small pieces and place in a food processor until the mixture is smooth. Remove and place in a large bowl. Add the mushrooms, leeks, peppercorns and season, thoroughly mix all ingredients together.
Take a 1.1 litre/2pt loaf tin and lightly grease with a little butter. Place bacon rashers on the bottom of the tin and place onto them the thyme sprigs.
Spoon the liver paté mixture into the tin and smooth the top. Cover with a piece of non-stick baking paper and then a piece of foil.
Place in a deep roasting pan and pour a little hot water into the tin to come about 5cm up the loaf tin. Cover with foil and place in a preheated oven for 1½ hours until mixture is completely set and top starting to brown
Carefully remove from oven and allow to stand for at least 20 minutes before turning out. Pour off excess juices, cover and place in the fridge to cool.
Serve sliced on warm walnut bread with plum sauce (lightly stew fresh plums with a pinch of cinnamon and squirt of honey).