A document must be certified when it is a copy of the original. The types of documents that need to be certified include copies of passports, photo ID and utility bills. To certify a document it must be signed and dated by a professional that is not related to you, does not live with you, and is not in a relationship with you. Those classed as professionals include councillors, dentists and teachers.
For more information visit
'How to certify a document'.