The Roman year finished in March. That's the original reason why tax is collected in the Spring. A big tax expert tells me this gives a new meaning to "beware the Ides of March".
In medieval times rents and debts fell due on Quarter Days: Lady Day on 25th March, Midsummer in June, Michaelmas in September and Christmas Day.
Lady Day, marking Mary being told she would give birth to Jesus, was the big one, partly because it coincided with Roman tradition. A lot of legal agreements started then.
Oops! But the actual calendar was wrong. The year was ever so slightly the wrong length. So in 1752 the UK adopted the more precise Gregorian Calendar.
Taking the Gregorian route meant adding 11 days to the date. And the start of the tax year was moved to 5th April, then later to 6th April.
Why move the tax year? Well, the government still wanted to get a full year of tax out of the public, of course. That meant a later start.
So the financial year has started on 6th April ever since, unlike US, France, Germany (1st Jan), Australia (1st July) and some countries which use 1st April.
