Legislation: EU law (Principal VAT Directive): Article 93 rate of VAT
The rate applicable to taxable transactions shall be that in force at the time of the chargeable event.
However, in the following situations, the rate applicable shall be that in force when VAT becomes chargeable:
(a) in the cases referred to in Articles 65 and 66;
The rate of tax applicable to a supply is linked in the first instance to the rate in force at the chargeable event. However, this is overridden in cases where the tax becomes chargeable at one of the alternative times provided for under Articles 65 and 66.