For same sex couples this means a civil partnership which has been legal in the UK since December 2005 under the Civil Partnership act 2004.

A civil partnership is formed when both individuals have signed a civil partnership document in the presence of a registrar and two witnesses.

This gives same sex couples the rights and responsibilities identical to a civil marriage, so once a couple register as civil partners they are entitled to the same property rights as married, opposite sex couples and will receive the same exemption on inheritance tax, social security and pension benefits.

A civil partnership also means you receive responsibility for any children your partner might have as well as responsibility for reasonable maintenance of your partner and children, tenancy rights, full life insurance recognition and next of kin rights in hospitals.

Just as a marriage or civil partnership between opposite sex couples, a civil partnership can only be dissolved on death, a formal dissolution similar to divorce or an annulment.

To be eligible for a civil partnership the couple must be the same sex and at least 16 years of age, with anyone below the age of 18 having parental consent (except in Scotland).

And, just as with a civil ceremony marriage, a civil partnership can’t be performed in places that are designed for or mainly used for religious purposes and there must be no religious service during the registration.

Before the registration each party will usually have to give notice to the appropriate authority and each must have resided in the UK jurisdiction in which they intend to register for at least seven days.

In most cases, immediately preceding the giving of notice, there will be a fifteen day waiting period. The proposed partnership is publicised and anyone can make a formal objection.

If there are no objections the registration authority issues a civil partnership schedule at the request of either party at the end of the waiting period. The civil partnership must then be registered within 12 months of the notice first being given.

*Elton John and David Furnish 'wed' on the very first day of same-sex unions being legalised in the UK. The two grooms celebrated in style along with a glittering celebrity guest list including Posh and Becks, Lulu, Greg Rusedski, Donatella Versace and Claudia Schiffer