Preheat the oven to 170 C / Gas 3. Season the pork roast with garlic, sea salt and pepper. Place in a roasting tin.
Bake the roast for 1 hour in the preheated oven. While the roast is baking, combine the pomegranate seeds and water in a large saucepan. Bring to the boil, then reduce the heat to low and simmer for 20 to 30 minutes, until the pomegranate seeds have broken down and released their juices. Press through a sieve to get as much juice as possible. You should have about 175ml of juice.
Pour the juice from the pomegranate into a saucepan and bring to the boil. Simmer over medium heat until reduced by half. Remove from the heat and mix in the balsamic vinegar, sugar and cinnamon.
After the roast has been in the oven for 1 hour, start to baste it with the pomegranate sauce, using a brush to apply to the top and sides. Continue to roast the pork until the internal temperature has reached 80 degrees C. Remove from the oven and allow to rest for 20 minutes before carving and serving.