Locking And Unlocking

The current-period VAT return includes all transactions dated on or before the current-period end date that have not been included in a locked VAT return for a previous period.

This ensures that all transactions are reported, with some possibly after the appropriate VAT return period, e.g. supplier invoices that are received late.

When a VAT return is locked, all those transactions are tagged as attached to that VAT return and will not, and cannot, be included  in future VAT returns.

If you lock e.g. the 31/05/2019 VAT return, then subsequently post transactions dated on or before 31/05/2019, these transactions will be included in the 31/08/2019 VAT return.

You can unlock the most recent VAT return, provided that it has not yet been submitted to HMRC using Prelude.

When a VAT return is unlocked, it becomes the current period and will determine its transactions as described above, and so will capture any subsequently-posted transactions as described above.