As civil partnership registration is a completely secular process, just like the civil marriage ceremony, you are prevented from having any religious service take place at the time of your registration.
A ceremony is not automatically provided when you register. Couples who wish to arrange for a ceremony at the time of registration should discuss this with the registrar when the initial arrangements are made. If you fancy walking down the aisle to the tune of a favourite piece of music you'll need to make sure it has no religious connotations as your ceremony has to be free of any mention of religion.
You will have the opportunity to say some words before you sign the registration schedule and you'll need to bring with you at least two other people as witnesses. If you did want to have a more spiritual ceremony, you could always arrange a separate humanist or other type of ceremony which would have special meaning to you. Couples who marry in civil weddings have the same limitations and often choose to have a humanist wedding ceremony as well as their civil wedding service.