The U.K. has very clear rules set by the HMRC that declare what an invoice document must include. In addition to the unique identification (invoice) number and a clear declaration of the word “invoice”, all documents must include the company information (name, address, and contact), customer information (name and address), description of the goods being charged, supply date of when the goods were provided, invoice date, total amount being charged as well as the applicable VAT amount and total amount owed.
Invoices by sole traders must include your own name as well as the business name being used. If you’re using a business name, then the invoice also must contain an address for the delivery of any legal documents. Limited companies are required to include the full company name on their invoices, and the names of all directors (if they’re to be included).
VAT invoices, which have to be issued if both you and your customer are VAT-registered businesses, include even more information than a general invoice. As previously mentioned, the invoice number has to be sequential for a VAT invoice. On top of all of the information already included in the invoice, they also need the VAT registration number of the supplier, the rate of VAT and amount of VAT chargeable (to be listed in sterling), any cash discount rates offered, and the reason for any zero rate of exemption. While most commercial invoices already meet the requirements of a VAT invoice, it’s important to make sure you don’t leave anything out.
If doing business with an EU member state, be sure to include the alphabetical code of the member state in front of the registration number - GB for Great Britain. The means of transport must also be referenced on the document.
Be sure to check the laws and regulations of any other country that you may be doing business with in order to stay compliant and avoid any trouble for you or your customers.