Complex sentence: In 2003 Octagon relinquished their ownership of TOCA and their subsequent control of the BTCC and a new company (BARC TOCA Ltd) was formed to manage the championship.
Split into simpler sentences: In 2003 Octagon relinquished their ownership of TOCA and their subsequent control of the BTCC. A new company (BARC TOCA Ltd) was formed to manage the championship.