Legislation will come into force on 1 January 2010 which clarifies that same-sex marriages in California which occurred before Proposition 8 are to remain valid in the state.

Governor Arnold Schwarzenegger signed the bill in October despite heavy opposition by Republicans, ensuring 18000 Californian marriages and all same-sex marriages which took place in other states before 5 November 2008, retain their legal status.

The bill also clarifies that couples who marry in other states in future will be able to benefit from the same advantages and protections that California provides to heterosexual married couples, though they will not be referred to as marriages in the state.

The author, openly gay Democratic senator Mark Leno, said: “When California offered marriage licenses to same-sex couples in 2008, spouses who were already married in another state or country were prohibited from re-marrying in California. Now those couples and their families will receive the rights and protections under the law to which they are entitled.”

Proposition 8 was approved in 2008 and overturned a previous Supreme Court ruling by adding a clause to the Californian constitution stating that marriage could only be recognised by the state if it were between a man and a woman, causing widespread controversy.

A constitutional challenge to Proposition 8 is due to commence in January.