Invoice requirements if payments received in advance
Payments may be received in full or in part before the completion of the supply of goods or services. In such circumstances you must issue a Value-Added Tax (VAT) invoice in respect of each payment.
You must issue a VAT invoice not later than the 15th day of the month following that during which each such payment was received. This does not apply in the case of intra-Community supplies of goods.
There are special rules for deposits.