Archbishop of Canterbury was a senior Christian clerical position in England.
Thomas Arundel served as the Archbishop during the late 14th and early 15th centuries. (AUDIO: The Doctor's Tale)
Thomas Cranmer served as the Archbishop until he was imprisoned in the Tower of London, tried and burned as a heretic. (AUDIO: The Battle of the Tower)
Using his psychic paper, the Eleventh Doctor convinced Craig Owens that he had a reference from the Archbishop of Canterbury in 2010. (TV: The Lodger)
Alternate timeline
In an alternate timeline created by the Elder Gods in the hope of destroying Earth, World War III broke out between the United States and its allies including the United Kingdom on the one hand and the Soviet Union on the other hand on 9 November 1989. The previous day, the Archbishop of Canterbury had appealed for calm and prayers as the British government placed all emergency services on standby. This timeline was ultimately negated by the Seventh Doctor. (AUDIO: Protect and Survive)