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The odd dates are due to events in the mid-18th century. The English quarter days are traditionally used as the dates for collecting rents (on, for example, agricultural properties). The tax system was also based on a tax year ending on Lady Day (March 25). When the Gregorian calendar was adopted in the UK in September 1752 in place of the Julian calendar, the two were out of step by 11 days. However, it was felt unacceptable for the tax authorities to lose out on 11 days' tax revenues, so the start of the tax year was moved, firstly to 5 April and then, in 1800, to 6 April.