'I found it in his storage and stole it," laughs Martha Wainwright. "I don't think it quite fit around his waist." The singer is referring to the silver and black-sequinned jacket she's wearing; a Liberace-esque number previously gifted to her brother Rufus.
Today, the jacket is teamed with a Martha Wainwright T-shirt ("Yeah, that's me from my first album cover"), while the Mikimoto pearl around her neck, Wainwright says, was a present Rufus bought their mother, Kate McGarrigle in Japan. My interviewee hesitates, then opens a tiny heart-shaped locket that dangles beside the pearl. "It's sad that there's nobody inside here," she reflects. "Maybe it's for the missing people."
Missing and lamented, certainly, is the aforementioned Kate McGarrigle. When the Canadian folk-singer known for the luminous harmonies wrought by she and her sister Anna died from cancer in 2010, it was just two months after the birth of Martha's first child, Arcangelo.
Fittingly, Wainwright's new album Come Home to Mama is largely a reflection on loss as viewed through the emotive prism of her own new motherhood. It's also the best record of her career by some margin.
When we meet in North London, Wainwright tells me that her cousin Lily, Anna McGarrigle's daughter, is outside babysitting Arc in his poussette. Born several months prematurely at London's University College Hospital, it was the aptly-named Arcangelo that got Wainwright through.
"Basically, I was forced into adulthood and responsibility," she says. "I was nurturing Arc and mourning Kate, but there was no option to crawl into bed and drink my way through this.
"At night I would sometimes excuse myself and go upstairs to fall apart and scream, but then I'd pull myself together because I didn't want to be crying in front of the baby. Brad [Albetta, Wainwright's husband and sometime record producer] would say, 'let's talk about this,' but I had to do it on my own."
Wainwright, 36, recorded her new album at Sean Lennon's home studio in New York City. Sensing it needed the feminine touch, she opted to have the gifted multi-instrumentalist and producer Yuka Honda, an ex-girlfriend of Lennon's, at the controls.
"People say women don't work well together but it couldn't have gone any better," says Wainwright. "Every day it was [she speaks quietly and warmly]: 'Don't worry – I'll handle it. Can I make you lunch? You look beautiful and you sing so well today.' I needed to be nurtured and Yuka truly did this."
Opting to have Honda rather than Albetta produce was also politic, for as Wainwright concedes, certain lyrics on Come Home to Mama were hard for her husband to swallow. There are references to make-up sex and marital difficulties, and at one point Wainwright sings, 'I built a ship of shit and directed it at you'. There's clearly been trouble at mill; loss and radical change can do that to a couple. Still, Wainwright maintains that, as both she and Albetta are children of divorced parents, they themselves are determined to go the distance.
Kate McGarrigle and Martha and Rufus's American folk-singer father Loudon Wainwright were divorced in the 1970s. Loudon, 66, has already released the superb Older Than My Old Man Now this year, and son Rufus's much- trumpeted, Mark Ronson-produced Out of the Game followed soon afterwards.
"As the little sister I'm used to coming last," says Wainwright. "Dad tends to come up with the best lyrics anyway, so what are you going to do? I don't want to feel overwhelmed by he and Rufus's stuff… I just try to scheme quietly in a corner. It's hard, though, because Rufus is a total music whore and he's on the phone going, 'You have to come to the studio and hear this!'"
Last out of the blocks it may be, but Martha Wainwright's latest could be the album that finally sees her trump her elder brother. She has sometimes lived in his shadow and it was hard not to see her 2009 tribute to Edith Piaf as a response to Rufus's 2006 tribute to Judy Garland, but Come Home to Mama is a quality-controlled and highly resonant work.
The title comes from a line in "Proserpina", the last song that Kate McGarrigle ever wrote. Wainwright says her mother had been reading a lot of Greek mythology in her final months, and that the song means a lot to her because it's a mother-daughter story based on the myth of Persephone.
"Kate believed in God but she also believed in Mother Earth," she adds. "She's singing 'come home to mama' as she nears the end of her life."
With regard to her own writing, it was when she penned "All Your Clothes" that Wainwright knew she was back. A dream-like ballad that takes the form of an imagined conversation with her late mother, it briefly finds Wainwright imagining Dr John playing piano through McGarrigle's fingers.
"My mom played great stride and she was really proud that there was a bit of New Orleans in there," she explains. "One day I was sitting in the kitchen and Dr John came on the radio. I saw Kate's hands and she came right through him to me. It felt like a gift.
"The song title felt like the right metaphor, too. Your loved one's clothes still have their hair on them, their smell, their shape…
"You know, Kate, Rufus and I were the same size, and oftentimes she would wear our clothes as a way of keeping us with her. It was so sweet that she wanted to put herself into them.
"Now, I spend a lot of time at her house in Montreal," Wainwright goes on. "Rufus gave it to me because he couldn't deal with it. I make a point of going without any luggage, and when I get there I literally step into Kate's shoes."
Wainwright says that there are plans for her, Brad and Arc to relocate to Montreal so that her son can have the French/English-language advantages that she and Rufus enjoyed. She also acknowledges that Kate and Anna McGarrigle's musical careers were very different to her own.
"They bowed out early, and they had this fuck-you attitude that everybody loved," she says. "They were like: 'We don't care if David Letterman wants to see us – we're staying in Montreal with our children.'
"Fortunately their songs were so good that people like Linda Ronstadt and Emmylou Harris were covering them, and that's what was keeping us kids. I think my career's going to be more like my dad's: up and down and longer," she adds.
Ah yes, Loudon, the inspiration for Martha's 2005 song "Bloody Mother Fucking Asshole." Has Kate's passing brought she and her father any closer?
"I think so. It made me need him more. And perhaps it made him feel like there was more room for him. When he saw me struggling with Arc's sickness and smallness, he took pity on me like never before and I think he felt bad.
At this a penny drops and Wainwright suddenly brightens. "Ha! Got him!"
"Come Home To Mama" is released on V2 on 15 October