If your client is a company, you can complete the declaration on their behalf and submit the return if both the following conditions are met:
you make a copy of the information before sending it
you have confirmation from the proper officer of the company (or other person authorised to act for the company), that the information is correct and complete to the best of their knowledge. Confirmation can be on paper or electronic
You, or your client, should keep a copy of the Company Tax Return and declaration, for the same duration as other records relating to the accounting period. You can choose to keep either a paper or electronic copy with an electronic signature.