The Former Archbishop of Canterbury, Lord George Carey, has argued that marriage equality should be opposed on the grounds that allowing marriages based “merely” on love and commitment would also justify polygamous unions and weddings between siblings.

In an essay titled ‘Love is Not Enough’, published by the think tank Civitas, Lord Carey argues “not all relationships are the same”.

He puts forward claims that marriage equality would enable incestuous marriages to take place – an argument recently given publicity by Lord Norman Tebbit, when he asked of same-sex marriage in an interview: “Why shouldn’t a mother marry her daughter? Why shouldn’t two elderly sisters living together marry each other? I quite fancy my brother!”

Lord Carey, who has previously accused David Cameron of creating a “broken society” through the same-sex marriage bill, writes: “Once we let go of the exclusivity of a one man-one woman relationship with procreation linking the generations, then why stop there?

“If it is ‘about love and commitment’ then it is entirely logical to extend marriage to, say, two sisters bringing up children together.

“If it is merely ‘about love and commitment’ then there is nothing illogical about multiple relationships, such as two women and one man.”

He adds: “Those of us accused of being on the wrong side of history can only plead with the Government to respect our concern that extending marriage to same-sex couples is not only unwise, but also sets a dangerous precedent.”

The Civitas publication, ‘The Meaning of Matrimony’, contains a number of contributions from various parties with a stake in the same-sex marriage debate, ranging from Stonewall executive Ben Summerskill and Peter Tatchell in favour, to Brendan O’Neill and Catholic Voices director Austen Ivereigh against.

There are also two essays from academics on the pro-equality side. One, from Anthropology professor Robert Lancaster, argues that same-sex unions have taken place in civilisations around the globe for thousands of years.

Mr Lancaster writes that early Greek Christian same-sex commitment ceremonies influenced modern wedding vows, arguing “same-sex relationships were the very models of ideal heterosexual marriages”.

Lord Carey is one of at least 86 peers who have requested to speak in the House of Lords during the debate on the same-sex marriage bill. Many are said to be planning to block the bill during the vote on on Tuesday 4 June.

Out4Marriage has launched the LobbyALord website in order to make it easy for members of the public to lobby Peers on the issue.