A proof of address can be a scan or a photo of a Bank Statement from a UK regulated Bank, or a Utility Bill from a regulated utility provider (not a mobile phone provider), clearly showing the following:
Your details – your full name and full address
Your account number - the unique reference to you
Date – when the document was issued (from within the last 90 days)
Sender – the name/logo and address of the issuing company
All of this information must be visible in one clear image.