|The Annunciation from the Black Book of Hours.|
For many centuries in England, Florence, and several other dominions in medieval Europe, the 25th of March was legally considered the first day of the new year. It was Lady Day, the feast of the Annunciation, when the archangel Gabriel delivered the news to the Virgin Mary that she would bear the Christ in her womb. The Annunciation is, of course, on the 25th of March because it is nine months from Christmas.
"Whan that the month in which the world bigan,
That highte march, whan God first maked man"
--Chaucer, the Nun's Priest's Tale, Canterbury Tales
The English so hallowed this beginning to the story of the Incarnation that Lady Day was retained as the new year, at least legally speaking, long after the Reformation until 1752, when the British government decided it was finally time to adopt the Gregorian calendar. Since 1582, Pope Gregory XIII's calendar reform had pushed the Catholic world to uniformly adopt the feast of the Circumcision, January 1, as the new year; previously, different realms had recognized Christmas, Lady Day, the Circumcision, and a plethora of other dates to commence it.
There is still one vestige of Lady Day's influence: in Britain today, the tax year begins on April 6. Because the country's transition from the old calendar to the new shaved off 11 days in 1752, many people threatened to riot if they weren't allowed the full year's cycle to prepare their taxes. The start of the year, therefore, was pushed 11 days to April 6.