"Unusual" VAT rate query (UK)?

Agreement to provide goods/services means nothing, it is the 'tax point' which defines when a the tax must be accounted for and if the tax point is before the rate rise, the rate will be 17.5% and after it will be 20%. Looking at goods, the basic tax point is when the goods are delivered but this can be replaced by the actual tax point if: Before delivery, an invoice is issued or payment made, whatever happens first, or if this has not happened, After delivery, an invoice is issued up to 14 days. However, if the basic tax point is before the change in rate, and the actual tax point is after, businesses have the discretion to use the 'special change of rate' provisions to charge at the lower rate.

The tax point is the time/date of supply or service. So... Item ordered 25 Dec, supplied 28 Dec, invoiced 7 Jan - VAT @ 15% Item ordered 25 Dec, supplied 4 Jan, invoiced 7 Jan - VAT @ 20%

You either use the delivery date or the invoice date (the invoice must be dated within so many days of the delivery date. This is called the tax point. It is nothing to do with the payment date!