Thanks for the advice.No need to take the marriage certificate, you both have the same name and address even though you may have a Maltese passport what you are doing is common practise don't worry about it, they know your NI number as well. When you renew your British passport send a copy of the maltese one all they will do is check the name is exactly the same in both, they won't ask you for a copy of your Maltese one but if you dont send a copy it will deny the issuing of the new British one.