I want to register the Civil Partnership as a “surprise” for my partner. Is this possible?

No. 

By law both parties to the registration of the Civil Partnership are required to submit notice forms to the registrar of the district in which the registration of the Civil Partnership is to take place. This means that both parties must be aware of this and independently complete and sign the declaration on form CP10 (184 KB pdf) to the effect that the information given is correct. Failure to give proper notice can result in registration of the Civil Partnership being postponed or prevented from proceeding.