The body you are registered with for Anti-Money Laundering should provide you with a list of acceptable documents.
You should keep a copy of one piece of photographic id (eg passport or driving licence) and one piece showing their current address - (eg utility bill (but not a mobile phone bill), bank statement or letter from the tax office). This should be dated no less than three months ago.
Also - the passport or driving licence should not be colour photocopied.