Blanch the pork before cooking to ensure that the finished dish will not be salty. Put the pork loin in a flameproof casserole and cover with water. Bring to the boil, then drain off the water and set aside.

Rinse and drain the beans. Place in the casserole and cover with fresh cold water. Do not add salt to beans during cooking as this will toughen them. Bring to the boil, then drain and rinse under cold running water and set aside.

Chop the onion. Trim the celery and scrape the carrots, then chop them roughly. Place vegetables and beans in casserole.

Mix the black treacle, tomato puree, mustard and allspice in a jug with 1/4 pint (150 ml) of cold water and freshly ground black pepper to taste. Add the mixture to the casserole and stir well to mix, then cover with plenty of cold water and bring to the boil.

Remove any scum from the surface with a slotted spoon, cover with a lid, then transfer the casserole to the Oven and cook for 2 1/2 hours, stirring occasionally, and adding more water if it becomes dry.

Add the pork to the beans, pushing it well down into the casserole. Cover and continue cooking for 45 minutes, until the beans are tender, then season to taste.

Lift the pork out of the casserole, carve into meat slices and arrange on plates with the beans.