This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

VAT Registration

Taxable supplies: determining liability to be registered

Liability to be registered is determined by the time of supply. In the majority of cases, the date given by the trader should be acceptable. However, if this is in doubt, the guidance in VATREG26000 may be helpful.

The rules for determining liability in the case of a TOGC differ slightly. More guidance can be found on this in VATREG29000.