A day ahead if possible mix together the garlic, smoked paprika and sage. Spread the mixture over the pork and set aside in the fridge overnight.
Heat the oven to Gas Mark 6, 200°C (400°F). Place the pork in a roasting tin and season with a little salt. Put the onions, carrots and celery around the pork. This will add extra flavour and colour to the gravy.
Place the joint in the oven and allow to cook for 50 minutes per kg. After the first 15 minutes reduce the heat to Gas Mark 5, 180°C (350°F). The crackling should be golden and crispy at this stage.
Peel and chop potatoes and a selection of vegetables. Place in a large bowl and drizzle with olive oil and season with salt and pepper. Transfer to a roasting tin, place in the oven and cook for 20-30 minutes until tender.
When the meat is cooked remove from the oven, transfer the meat to a chopping board, cover loosely with tin foil and allow to rest for 20 minutes.
To make the apple and blueberry Sauce, place the apples, blueberries, butter, sugar and a tablespoon water in a small saucepan. Bring to the boil then reduce the heat and cook over a low heat for 10-15 minutes, stirring occasionally, until very soft. Taste before serving and add a little more sugar if needed.
To make the gravy: stir the flour into the juices in the roasting tin. Place over a medium heat and continue stirring with a wooden spoon. Gradually add in the stock or water and redcurrant jelly, stir until it thickens. Taste and season. Pour through a sieve into a gravy boat. Discard the vegetables that were cooked alongside the roast.
Slice the pork and serve with the roasted vegetables, gravy and apple and blueberry Sauce.