Rowan Williams, the Archbishop of Canterbury, in an elegiac, filmic farewell to the building – "a purpose-built factory for prayer" – and his job, is seen wandering through the enormous space from attics to crypts, turning the whole space into a valedictory sermon. His film for BBC2, Goodbye to Canterbury, to be broadcast on New Year's Day, is far from a tourist trail around the cathedral's medieval glories. The Guardian's Andrew Brown once described trying to follow Williams's thought processes as like watching "a jellyfish dropped in a jacuzzi". He compares the iconoclasm of the English Reformation, when hundreds of medieval carvings of saints and angels in the cathedral were decapitated, stained glass shattered, and acres of wall paintings destroyed, leaving only a few survivors in the crypt, to images of a smashed Starbucks window, the destruction of the giant Buddhas of Bamiyan, and a defaced image of Colonel Gaddafi. "When today's idols, false or otherwise, are built up and smashed down, I'm glad to have this place to retreat to, and remember that these are arguments that never go away. It's a mistake we make too easily to think we've progressed between the moral questions of the past, but what we can put behind us is institutions that have failed." He reflects: "Institutions develop because people put a lot of trust in them, they meet real needs, they represent important aspirations, whether it's monasteries, media, or banks, people begin by trusting these institutions, and gradually the suspicion develops that actually they're working for themselves, not for the community. At the end of the middle ages, nobody would ever have expected the monasteries to vanish from the scene within a generation – yet they did, change does happen." Recalling his first crisis within weeks of taking the job, his personal opposition to the war in Iraq, and then his reluctance "to sound off from a distance" when British troops were risking their lives on the ground, he found he was satisfying nobody on either side. "Being unpopular, taking the rap, aren't accidental side-effects, they're the stuff of the job." He got off comparatively lightly, he considers, reflecting on the fate of Thomas Becket, murdered in the cathedral on 29 December 1170. In the film, he often seems a lonely figure, as he did to many observers of his time as archbishop, when he wrestled with problems from the appointment of gay priests and women bishops to the revelation in the census that faith of any kind is in freefall. Kneeling by the 15th-century tomb of Henry Chichely, Archbishop of Canterbury and chancellor to Henry V, which shows him as a prince of the church on the upper level and a worm-gnawed corpse below, Williams grimly translates the carved Latin motto: "Here is my tomb, look into your mirror." The tomb was deliberately set opposite the seat for his successors at Sunday service. Gazing around the great golden space – mysteriously scoured bare for the cameras of the usual heaving mass of clergy, worshippers and tourists – he perches on the great stone archbishop's chair, barely taking up half the seat. "It is physically impossible to fill this throne, and that shouldn't be surprising," he reflects, "since it's certainly spiritually impossible to fill it also. The first time you sit here you realise that you have countless new ways of getting things wrong, countless new responsibilities and expectations laid on you – and the likelihood is that you're going to get most of them wrong." His surroundings will be almost as glorious in his new post of Master of Magdalene College in Cambridge, which he takes up in a few days, but hopefully the responsibilities and expectations slightly lighter.