Members of the House of Lords raised fears of polygamy, incest and lesbian Queens as they staged a last ditch attempt to kill off the government's gay marriage Bill on Monday evening.
The Marriage (Same Sex Couples) Bill was easily passed by the House of Commons in May despite the opposition of a majority of Conservative MPs - thanks to the support of Labour and the Lib Dems.
Opponents of allowing gay couples to wed have pinned their hopes on a move by crossbencher Lord Dear to force a vote on the Bill's second reading on Tuesday. The attempt by peers to wreck a piece of government legislation passed by the elected Commons is a break with convention that has been condemned by several peers and MPs.
Lord Dear recruited Alice in Wonderland and Humpty Dumpty to his cause when he said to allow gay marriage was to fall "through the looking glass" as "tolerance can be overstretched".
Citing widespread protests in France against gay marriage, Lord Dear added: "The majority view should prevail, especially when the minority is tiny and the overwhelming majority is affronted."
Just as David Cameron found his MPs were split on the issue, Tory peers led the attacks on his Bill.
Former Conservative cabinet minister Lord Tebbit repeated his claim, a worry shared by many anti-gay marriage peers, that legalising gay marriage would open the door towards polygamist or incestuous marriages. He also worried about what would happen if a future Queen were a lesbian.
"There is, I believe, no bar to a lesbian succeeding to the Throne. It may happen. It probably will, at some stage. What, then, if she marries and her partner bears a child by an anonymous sperm donor? Is that child the heir to the Throne?" he said.
Baroness Knight, who as a Conservative minister in 1988 introduced the Section 28 law which banned the "promotion" of homosexuality, said while gay people were "very artistic" they should not be allowed to get married.
"This Bill is either trying to pretend I can change men into women, or vice versa, or it’s telling us that children don’t need a father and a mother, or thirdly it is saying that a secure framework for children to be brought up in is not important any more," she said.
Tory Lord Framlingham said the gay marriage Bill showed the country had "lost its moral compass". And Conservative Lord Waddington said the introduction of same-sex marriage in other countries had led to a "precipitous" decline in straight people deciding to get wed.
He added: "Cameron thought it was worth picking a fight with his best supporters. It was a big mistake."
It was not just Tory peers who announced they planned to vote against the legislation. Crossbencher Lord Craig of Radley was worried that gay marriages would lead to a "threesome or foursome union". And Labour peer Lord Anderson of Swansea said it would cause "increased pressures for polygamy".
And Lord Hylton had a deeper problem. He was unhappy that gay people called themselves gay. The crossbench peer said: "I regret very much that the fine old English word 'gay' has, in my lifetime, been appropriated by a small and vocal minority of the population. The result is it can no longer be used in its original and delightful meaning."
"Now under the pretet of securing equality the government is proposing to change the word 'marriage'. It is surprising the leaders of the Conservative Party, who might be expected to uphold tradition, should lend themselves to this effort."
In his first major intervention in the debate, the Archbishop of Canterbury condemned "sickening" homophobic language and expressed "sadness and sorrow" for how the Church had teated gay people in the past.
But said he could not support the Bill as it "weaken" marriage and society. He said: "It confuses marriage and weddings. It assumes that the rightful desire for equality, to which I have referred supportively, must mean uniformity, failing to understand that two things may be equal but different."
Although the Bill is expected to pass the vote on Tuesday, both sides believe it will be close. In a last minute bit of lobbying, pro and anti-gay marriage campaigners staged rallys outside parliament as peers debated the legislation.
Lord Fowler, a former chairman of the Tory Party who supports the Bill, told peers gay people, who continued to suffer discrimination, had the right "to expect what we all expect; nothing more, but certainly nothing less."
"Parliament should value people equally in the law and enabling same-sex marriage removes a current inequity," he said. "For some of us, that is a fundamental moral issue."
And Viscount Astor, the stepfather of David Cameron's wife Samantha, said it would be "quite wrong and highly damaging to the reputation" of the unelected Lords if it rejected a Bill passed overwhelmingly by the Commons.
Labour's Lord Smith, the first openly gay MP, said voting for gay marriage would "right a long standing wrong".
He said: "It will recognise the equal dignity and worth of all our lesbian and gay citizens. It will challenge the prejudice that is still all too prevalent in our society. It will say, quite simply, that love matters and equally so for everyone."