As an agent, do I need to obtain a declaration and keep a copy of my client's end of year return before I file it online?
As the accuracy of the figures on the return is the responsibility of the client, HM Revenue and Customs (HMRC) suggests that you may want to take a copy of the return that is being submitted and ask your client to formally approve it. HMRC don't specify the format of the copy - it can be an electronic version or paper copy.