Sprinkle the pork belly and stewing pork with the rosemary and cayenne and leave to marinate for a few hours or preferably overnight.
Fry the sausage pieces until the start to brown. Remove with a slotted spoon and keep them to one side.
Tip the other pork bits into the hot fat and keep the pan over a medium heat until they have picked up some colour.
Add the onion, celeriac, parsnip, celery, carrot and garlic and cook gently for about 20 minutes with a lid on, stirring regularly.
Stir in the tinned tomatoes and chicken stock, then bring to a simmer and keep very gently bubbling with a lid on, topping up with water if necessary, until the pork is beginning to soften - this can take up to 2 hours.
Stir in the lentils and sausage and top up with water again, enough to cook the lentils, if needed.
Once the lentils are cooked (about 30 minutes) and the pork is totally tender, have a look at the consistency. If it looks a bit thin, let it bubble away until you have a consistency that appeals and conversely add a bit more water if you think it could do with it. Season and serve