The Castellan was in charge of the Chancellery Guard by the time of the Eleven's escape from the Capitol prison facility. Before becoming an ensign, he was hypnotised to allow the Eleven's escape in the future. The Eighth Doctor said that, during his last visit, the castellan had not even been a captain yet.
He was in charge of Kiani's interview with the Eleven and sent guards once he worried that the Eleven was becoming bored of her. He alerted Cardinal Padrac when the Eleven escaped and later had his hypnosis discovered by the Doctor, revealing that he had helped in the escape. (AUDIO: The Eleven)