Alex Salmond pushed against gay marriage, says Nicola Sturgeon

The former first minister said Mr Salmond “became increasingly hostile” to the idea until he was “implacably opposed”.

Writing in her new memoir, she recalled “heated arguments” in the months following a consultation on the issue, which ended in December 2011.

“It took months for the issue to come to Cabinet,” Ms Sturgeon, who was then Deputy First Minister and health secretary, wrote.

“Partly this was down to the high number of responses, but it also reflected Alex’s reluctance. I was never certain how much of his social conservatism came from genuine belief as opposed to political opportunism. Either way, he became increasingly hostile. This resulted in one of the most heated arguments we ever had.

“We were in his study in Bute House on a Tuesday afternoon, just before a meeting of cabinet. I had collared him to say I wanted the equal marriage decision on the agenda the following week.

“What started as a calm discussion very quickly descended into a shouting match. Alex very rarely raised his voice to me - or vice versa - so I knew that I had a real battle on my hands to get him to agree. He was implacably opposed.

“Couldn’t I see that pushing gay marriage would lose us support in the referendum? I countered that not doing so would lose us support too: one of the concerns many people had about an independent Scotland was that the forces of social conservatism would hold too much sway.

“And anyway, surely it was a decision we should reach on principle, not from crude political calculation?”

Ms Sturgeon later recalled a meeting of the Cabinet on July 17, 2012, in which Mr Salmond “dug his heels in”.

She wrote: “He claimed that the law would be a slippery slope and made arguments that seemed rooted in the prejudice which had put Section 28 on the statute book.

“He claimed that priests and ministers would be forced to conduct gay marriages despite the teachings of their faiths; that children would be taught about gay marriage against the wishes of their parents; that the freedom of speech of those who believed that marriage could only be between a man and a woman would be eroded; and that we would haemorrhage independence support if we went ahead.”

Mr Salmond later “very reluctantly” conceded the issue, Ms Sturgeon said.

She wrote that Alex Neil, who succeeded her as health secretary, then kept the legislation on track.

The Marriage and Civil Partnership (Scotland) Act was eventually passed by the Scottish Parliament in February 2014, and the first same sex weddings took place 11 months later, on New Year’s Eve.

“A country that just 35 years earlier still criminalised sex between men became the 17th nation in the world to legalise marriage for gay and lesbian couples, to recognise, and proclaim with pride, that love is love,” Ms Sturgeon wrote. “It was a joyous moment.”