The ‘Leper Window' and 'Weeping Chancel'
A 'leper' window or hagioscope is fairly common feature of medieval churches. They were provided so that lepers, who were forbidden to mix with the general population, could observe the elevation of the Host during the Mass through the window. Leprosy was brought to Britain by soldiers returning from the Crusades around 1200, and ‘lazar' houses were built outside cities, including one in Knightsbridge, so it is possible that a small leper colony may have existed in Perivale. A more prosaic explanation of the window is to provide more light to the priest reading the divine office.
The Chancel deviates slightly but definitely from the east-west line of the nave, with a distinct 'tilt' to the left. This is more than can be accounted for by chance, and is obvious when pointed out to onlookers, although difficult to illustrate in a photograph! This is another fairly common feature of medieval churches, and was thought to represent the leaning of Christ's Head upon the Cross. Another recent explanation relates to the variable date of Easter, since the exact eastern axis of the chancel would have been determined by the position of the rising sun on Easter Day.
The small 'leper window' on the left of the main south chancel window The 'leper window' from the interior, with stained glass showing the Crucifixion The 'Weeping Chancel'. The photo is taken in the central axis of the nave. The right chancel wall, but not the left, is easily visible. Assymetry in the chancel roof and arch caused by the Weeping Chancel multiple lightbox galleriesby VisualLightBox.com v6.1