Lastly, please get client agreement if ok to date invoice on 25th Dec rather the 28th Dec eventhough this invoice is issued on the 28th Dec. Suggest to explain to them that need to take this invoice into Dec 15 month accounts & therefore need to date on 25th Dec.
Please avoid changing the invoice date on the copy of invoice that is being sent to the client (outside of BST) as it will differ from the BST invoice date.