UK fiscal celandar - Origin

The 6th April starts the UK fiscal calendar year.
Why is that?

In British and Irish tradition, the quarter days were the four dates in each year on which servants were hired, and rents and rates were due. They fell on four religious festivals roughly three months apart.

The English quarter days (also observed in Wales) were:

Lady Day (March 25)
Midsummer Day (June 24)
Michaelmas (September 29)
Christmas (December 25)


Lady Day was also the first day of the year in the British Empire until 1752.
The British tax year still starts on 'Old' Lady Day (6 April under the Gregorian calendar corresponded to 25 March under the Julian calendar).

The logic of using Lady Day as the start of the year is that it reckons years A.D. from the moment of the Incarnation, which is considered to take place at the moment of the conception of Jesus at the Annunciation rather than at the moment of his birth at Christmas.

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