Schedule 20 is subject to adjustment, and additional overseas relationships may be added as more jurisdictions across the world bring in civil partnership or same-sex marriage legislation.

The following unions were created after Schedule 20 was last updated: The Act was announced in the Queen's Speech at the start of the 2003/2004 legislative session, and its full text was revealed on 31 March 2004.

It received royal assent on 18 November 2004 and came into force on 5 December 2005, allowing the first couples to form civil partnerships 15 days later.

High-profile Conservative MPs who voted against the Civil Partnerships Bill included Iain Duncan Smith, Ann Widdecombe, Bob Spink and Peter Lilley.

[10] An amendment tabled by Conservative MP Edward Leigh proposed to extend the property and pension rights afforded by civil partnerships to siblings who had lived together for more than 12 years.

[16] Labour and the Liberal Democrats issued a whip against the Leigh Amendment, and only two MPs from each party rebelled to vote in favour of it.

[10] On 24 June 2004, during the discussion at the report stage in the House of Lords, Conservative peer Baroness O'Cathain moved an amendment to extend eligibility for civil partnership to blood relatives who had lived together for a minimum period of time.

This requirement was removed by Parliament in March 2019, and since 2 December 2019 couples irrespective of sex can register their intent to form a civil partnership.

[20] In June 2018, the Supreme Court ruled in the Steinfeld–Keidan case that restricting civil partnerships to same-sex couples was discriminatory and mandated that the Government change the law, although did not set a timeline for doing so.

[25][26][27] The regulations came into effect on 2 December 2019, the date on which opposite-sex couples could register their intent to form a civil partnership.