1. Remove the string from the brisket. Unroll the meat, place on a non-metallic dish and coat with the steak rub. Cover and leave in the fridge for 12-24 hours.
2. Preheat the oven to 150°C, gas mark 2. Place the sauce ingredients into a roasting tin large enough to hold the meat laid out flat. Season with black pepper and mix well, then add the beef and any juices to the tin.
3. Spoon the sauce over the meat. Top with a piece of scrunched-up, damp baking parchment, followed by a large piece of foil. Seal tightly around the edges and place into the oven for 3 hours. Remove from the oven and leave, covered, in the tin until required. If longer than 30 minutes, cool completely and refrigerate.
4. Light or preheat the barbecue, griddle or grill. Remove the meat from the sauce and place it onto the barbecue rack. Cook for 20 minutes, turning frequently, until the meat is piping hot throughout.
5. Meanwhile, bring the sauce in the roasting tin to the boil over a high heat and simmer vigorously for 20 minutes, or until thickened and reduced by about two-thirds. Strain through a sieve into a jug, pressing well with the back of a spoon to release all the juices. Serve the meat, thinly sliced, with plenty of sauce to spoon over, garnished with the remaining thyme.