From the Civil Partnership info website, here are the differences:
Differences between Civil Partnerships and Civil Marriages
Although a civil partnership is essentially viewed as a ?gay marriage?, between same sex partners, the reason it is not called a ?gay marriage?, is that there are a few differences between a partnership and a marriage on a technical level.
A civil partnership becomes legal when the registration certificate is signed by both partners. This does not mean that it must be signed during a ceremony that is public or during any specific event. This allows the partner to enter into the partnership on a private basis. There need be no words exchanged. During a civil marriage, typically words are exchanged and then the register is signed.
A vast difference between a civil partnership and a civil marriage is that a civil marriage almost always contains religious aspects during the marriage. The word marriage is a religious word in itself. Additionally, a clergy can perform civil marriages, whereas only specified registrars can perform a civil partnership.
There are also vast similarities between the two. In both a civil partnership and a civil marriage, the couples are required to give public notice of the intentions. The records of both are kept as official and public documents with the registry offices. Couples are required to wait a total of 15 days prior to registration but after giving notice of the partnership. After the 15 day waiting period the registration is given, and then it is valid for one full year after the date of registration.