According to HMRC you should have the following:
You must clearly display the word 'Invoice' on the document.
You must also include:
- a unique identification number - (Invoice Number)
- your company name, address and contact information
- the company name and address of the customer you're invoicing
- a clear description of what you're charging for
- the date the goods or service were provided (supply date)
- the date of the invoice
- the amount(s) being charged
- VAT amount if applicable - (only if you are VAT registered)
- the total amount owed
Sole Trader Invoices
- you must include your name and any business name being used
- an address where any legal documents can be delivered to you if you are using a business name
Limited Company Invoices
- You must include the full company name as it appears on the certificate of incorporation.
- If you decide to put names of your directors on your invoices, you must include the names of all directors.