“Tax point” for VAT

The time of supply is the earlier of:
the date when the supply is ‘really’ made, referred to as the basic tax point;
the date when a tax invoice is issued in respect of the supply; and
the date when payment is received for the supply.
There are a number of refinements to be borne in mind in applying this basic rule, particularly the 14-day rule, and there are also special rules for certain kinds of supply.
If a VAT invoice is issued within 14 days of the basic tax point, the basic tax point can be ignored in fixing the time of supply and the date when the invoice is issued is used instead.
The invoice must be a proper VAT invoice and must be issued by the supplier to their customer.
It is possible to opt out of the 14-day rule, but this must be notified in writing to HMRC.