The clocks go forward on the last Sunday of March, at one in the morning, when 1 am becomes 2 am and that hour simply does not exist. British Summer Time then runs until the last Sunday of October. It is the change people notice most, because it moves an hour of daylight into the evening overnight and takes an hour of sleep to pay for it.
March closes the first calendar quarter of 2029 on the 31st and takes the tax year to within days of its own end. That mismatch of five days between the two year ends is a genuine British peculiarity, inherited from the switch to the Gregorian calendar in the eighteenth century and never tidied up since.
March 2029 runs to 31 days and completes the first quarter of a year of 365 days. The tax year that began the previous April has less than a week left to run once the month ends, and the new one starts before April is a week old.