According to Amy's soon-to-be ex-husband Blake Fielder-Civil, the singer took 2g of the Class A drug from the supermodel's handbag at a star-studded bash in New York so the pair could snort it in the toilets.
"Kate Moss and another supermodel were there, as well as Hollywood actresses. Kate had told Amy to get a $10 note out of her handbag to snort lines with," he said.
"But Amy told me she found 2g of cocaine in there - so she nicked them. We did some in the toilets and had sex, but we did the rest in front of everyone. Kate was so drunk; she never noticed it was missing."
The 27-year-old ex-convict claims cocaine was freely available to guests at the bash, held at the Gramercy Park Hotel just weeks after Blake and Amy married in Miami in May 2007.
Funded his addiction
"There was plenty of cocaine on a table in the room available to everyone."
Blake has also claimed Amy became addicted to heroin the first time she tried it and took to the illegal substance "like a duck to water".
"I'd been smoking heroin on my own, but never in front of her. I got a bit for myself, and she looked at me and said, 'Can I have some?'
"I was out of my mind on drugs and I said, 'Of course'. She inhaled the heroin and then just sat back, smiled and her eyes went a bit funny. She said, 'I can see why you take this.' Amy took to heroin like a duck to water, same as me," he added.
Blake also claims the 25-year-old pop star funded his ongoing addiction when he was in prison and would transfer money - sometimes up to £1 000 ($1 900) a week - into a bank account for him.
"Whenever I needed heroin I would make a phone call to Amy. Sometimes I only needed a £20 a day hit, but other times I was taking it constantly and could spend £140 a day."
Blake was jailed for 27 months last August for perverting the course of justice and grievous bodily harm. He was released from prison last November.
The former couple were recently granted a decree nisi in their divorce and their separation will be legally finalised in just over four weeks.