EA guidance:- http://www.environment-a...ness/sectors/143926.aspx ..........You may be asked to prove you are an authorised person when collecting or transferring waste to someone else. You can do this by using your registration certificate or tell your customer to check the public register........ If I was a client, I would verify the registration via the public register. The above guidance, by implication is that it is not mandatory ( by law) to display the certificates.