Complex sentence: In 2003 Octagon relinquished their ownership of TOCA and their subsequent control of the BTCC and Gow returned to once again head-up and rebuild the championship after it had floundered under the control of the previous management.
Split into simpler sentences: In 2003 Octagon relinquished their ownership of TOCA and their subsequent control of the BTCC. Gow then returned to once again head-up and rebuild the championship after it had floundered under the control of the previous management.