Like in most EU countries, UK Intrastat returns are filed monthly. They follow the calendar month.
The due date to file these returns is the 21st day of the following month. If this due date falls on a Sunday or public holiday, the date is shifted to the previous working day.
In case a business is submitting VAT returns with a non-standard VAT period, the reference period for their intrastate return can be either the month when the goods arrived or the month when the tax point occurs.