A NEW category will soon appear under the hatched, matched and dispatched columns — and Sir Elton John and his lover, David Furnish, will be one of the first couples to announce their “marriage”.

The Civil Partnership Act 2004, which takes effect on December 5, creates a legal status of “civil partner” between same-sex couples. It is not identical to marriage and, to make the law less controversial, religion has been excluded — the ceremony will take place in a register office, not a church. Same-sex couples can already have religious blessings and last year some local authorities implemented the registration of same-sex relationships. However, what is different about the Civil Partnership Act is that it has legal ramifications.

Once registered, for most purposes, the couple are regarded as “spouses”. This means that legislation that affects spouses — family law and tax provisions being the main ones — will need to be read as also covering same-sex couples.

As with marriage, the registered partnership will make any will null and void unless it is made specifically in contemplation of entering into the civil partnership. And, as with divorce, ending the civil partnership will mean that the partner no longer benefits under the will. The grounds for dissolution will be “irretrievable breakdown”, but there will not be the option for a same-sex partner to plead adultery.

As with married couples, a breakdown in the relationship could lead to one partner claiming maintenance, including for children. Ellen DeGeneres’s former girlfriend was reported as considering taking legal action “for revenge and riches” against the actress and her new lover, the Ally McBeal actress Portia de Rossi. Such claims are likely to be more common once the new law comes in.

The partnerships also affect the rules if a person dies without having made a will. But, absurdly, this will apply only if the civil partnership has been registered for more than two years before the death. The partner will then be regarded as the “spouse” and be able to inherit the first tranche of the estate.

Many employers and insurance providers have recognized same-sex relationships for years. In the workplace, benefits such as travel insurance and healthcare can already apply to same-sex partners. However, to take advantage of these benefits, the person has to “come out” at work.

The recently introduced law on discrimination against a person at work on the ground of his or her sexual orientation specifically excludes from its remit claims that same-sex partners are not getting the same benefits as those conferred on married staff. Registering a civil partnership will therefore close that loophole and entitle the registered partner to benefits.

Registered same-sex partners will enjoy tax advantages akin to those of married couples. A partner will be entitled to receive benefits on death free of inheritance tax and make gifts to their partner free of capital gains tax. This opens up more opportunities for tax planning for same-sex couples.

Unmarried heterosexual couples are in a similar position to unregistered same-sex partners. The “common law” husband and wife is a myth: this means that there are no tax breaks available. Nor do they have any rights under the intestacy legislation, unless the survivor can prove that he or she was dependent on the deceased partner. Therefore, it is essential that unmarried or unregistered couples write a will setting out provision for the surviving partner and any children, including stating that the surviving partner should be recognized as the guardian of any children, especially if the children are not blood relatives.

The civil partnership legislation allows same-sex partners to formalize their relationship and presents tax planning opportunities and protection under the intestacy rules. However, for same-sex couples to take up these benefits, they will have to make their relationship public. They will then have to “come out” at work if they want their partner to be entitled to be treated as a “spouse”. Though society appears to have become more tolerant, and laws are in place to protect against discrimination, there are still many lesbians and gay men who make concerted efforts to conceal their sexuality