The Worshipful and Ancient Law of Gallifrey was a book that was once stored in the Panoptican Archive on Gallifrey. It was also the 'key' to Shada the Time Lord's prison planet, when the pages were turned within a TARDIS it would take the craft to Shada. (DW: Shada, WC: Shada, BFA: Shada)
Removal from Gallifrey and subsequent use
It was stolen from Gallifrey by Salayvin, who subsequently requested that the Doctor return it to Gallifrey for him. Following this meeting it was stolen by Skagra who utilised it and the Doctor's TARDIS to travel to Shada.(DW: Shada, WC: Shada, BFA: Shada)