Don't be put off by "terrine" in the title: this is a very easy dish, which might make people think you've gone to a lot of trouble! I am not sure how long this takes to make as I have never bothered to time it.
NOTE: Do the dish the day before, or even 2 days before: it improves on standing.
For this, use the brand of pork sausages you like best -- a good quality. The real British breakfast sausage is what you want.
Put oven on 350 deg F/180 deg Celsius.
Put the pork sausage meat in a bowl, then add the rest of the ingredients except the bacon. Mix well.
Using a medium bread tin or terrine, grease lightly, then line it with the bacon (the streaky type are the strips with a fair amount of fat marbling, more so than shoulder bacon).
Spoon in the meat mixture, pressing in lightly, and smooth with the back of a spoon.
If there are any flaps of bacon visible, fold over the terrine.
Bake for 1 hour plus, until slightly risen and firm. Let it cool to warm. Don't pour off fats and liquid now, as much will be reabsorbed into the terrine. You can discard extra fat when you unmold it later.
(You could also bake it more carefully, by putting the terrine in a larger dish, and filling the larger dish with hot water, to come halfway up the terrine).
Using a cleaned clay brick, wrap it in 2 thicknesses of foil and put on the terrine to weigh it down. When cold, keep in fridge overnight.
To serve, unmold and garnish to taste, and serve with mustard or sauce of your choice. Can be heated in the oven, and served with veggies and a carb, for the main meal.