Time of supply or tax point in the Invoice

The tax point (or ‘time of supply’) for a transaction is the date the transaction takes place for VAT purposes.

You need to know this because, for example:

•  it’s included on VAT invoices 
• it tells you which VAT period the transaction belongs to
•  it tells you which VAT Return to put the transaction on 

 The tax point can vary, but is usually the following.

The date of supply is:

• for goods - the date they’re sent, collected or made available (eg installed in the customer’s house) 
• for services - the date the work is finished

Source: https://www.gov.uk/vat-record-keeping/time-of-supply-or-tax-point