Paul McCartney is carving a mushroom Wellington. Except he’s doing it wrong. He cuts through the pastry too quickly and the photographer standing on the other side of the table can’t get her shot. Then a small decorative vase is in the way. Fashion designer Stella McCartney, Paul’s daughter, films everything for her Instagram Story. “End animal agriculture!” she says, panning her phone over the spread of vegetarian dishes and zooming right in on the pastry. Stella is now also in the way of the shot.

So, I’m at a festive lunch with the McCartney family – and a few “really cool people”, according to Paul: musician and youth advocate Loyle Carner , 18-year-old climate activist Anna Taylor , and zero-waste restaurant founder Doug McMaster . We’re ostensibly here to celebrate the launch of a limited edition vegetarian roast from Linda McCartney Foods, the vegetarian food brand founded by Paul’s first wife, a vocal animal rights activist up until her death from breast cancer in 1998. But today isn’t just about a photogenically sliced roast. We end up discussing the climate crisis, in a conversation underpinned by the bizarre reality of sitting around a table with one of the last living Beatles.

By this point though, Paul has sliced the entire Wellington. Another one is sent for from the kitchen, and someone suggests he try carving the vegetarian roast – the table’s centrepiece, served with mushroom duxelles on a marbled ceramic plate – instead. Photographer Mary McCartney, who sits on the opposite end of the table to her sister Stella, says that the lighting would be better if Dad were on the other side. Paul smiles his Can’t-Buy-Me-Love smile. “I just love carving!” he laughs. Mary makes him swap seats. The photographer politely suggests Stella pause her Instagramming for a moment so that she can get the photo of Sir Paul McCartney CH MBE slicing a veggie roast.

Soon, we’re trading ideas back and forth. First, Taylor points out that “The media focuses on Western problems, on white European problems, which means “people in the global south and ethnic minorities are just left out of the discussion when they’re the ones that are suffering the most”.

Talk quickly turns to news coverage of the environmental crisis, kicked off by Stella positing her late mother’s brand as “a revolutionary concept”. This lunch could have been “a conventional Christmas roast”, she continues, “but it’s a much more timely conversation to take advantage of the fact that, for the first time in the history of our lives, we’re witnessing human beings around the world waking up to this issue.”

When I arrived earlier this morning at the airy shoot location in north west London, the space buzzed with assistants wrestling photography screens and catering staff eager to offer glasses of Engish sparkling wine. Taylor arrived shortly after me, fresh from her first term at university, and McMaster came straight from the site of his new Silo restaurant. We made small talk around a beautiful platter of crudites and homemade oatcakes, none of us sure what to expect. Loyle Carner told me that when the Linda McCartney Foods publicist first contacted him about the lunch, he didn’t realise that he was being invited. “I said, ‘Great, I’ll look out for it online then,’” he recounted, laughing. Even cool people don’t expect to be invited to lunch with Paul McCartney.

The table nods in agreement. Paul says: “It changes really slowly, so all you can do is what the kids are doing, and protest and do everything you can. I was thinking the other day, ‘Oh, it’s going to turn everyone off’” – a reference to both the student climate strikes and Extinction Rebellion’s non-violent direct action tactics – “and sure enough it is: ‘Oh they’re naughty, they’re making noise, it woke me up.’ But it’s like, what about the suffragettes? They were dying for it and now women have rights. Well, some women – not everyone.”

This love for the natural world and domestic life forms the core of the Linda McCartney brand, which still promotes its products as coming from ‘Linda’s kitchen’. Paul, Mary and Stella consult on the business, including its drive to use entirely plastic-free packaging by 2021 and the introduction of new vegan products, aligning it both with veganism’s growing popularity and the modern environmental movement. On the day of our lunch, Extinction Rebellion protestors are four days into their two-week shutdown of central London .

Paul went veggie in the mid-70s after seeing lambs “gambolling” outside while he ate a Sunday roast , but credits Linda as the driving force behind their family’s conversion. She launched the food business in 1991, focusing on veggie versions of homely comfort foods like lasagna and burgers, then expanding the range. Despite her day job as a music photographer – and performing with Paul in Wings for much of the 1970s – Linda was a staunch earth mother. She and Paul raised Stella, Mary and their siblings on a farm in East Sussex, surrounded by acres of countryside, horses and pet chickens. “The fox got all of them, wiped them all out,” Paul says wistfully. “But we loved those little chickens.”

In practical terms, that looks like Stella refusing to use fur or leather in her designs, and recently shooting an ad campaign featuring Extinction Rebellion protestors. Throughout our lunch, Mary and Stella talk loud and fast about everything from dodgy salmon farms to wild ponies and antibiotics in beef, desperate to get across the importance of helping more people eat less meat. Paul sits in the middle and nods good-naturedly, the dad between two chatty sisters.

“There is a connective tissue between what you’re seeing in the climate strikes and how Mum approached things,” Stella agrees. “That was actually at the core of it – there is a loving desire to make change and give information and solutions.”

“Yeah, she would have been out front, she would have been out there,” Paul says. “You can look at all these protestors and go, ‘They’re out of step, they’re not doing what ordinary people do.’ But then you would still have slavery, you would still have women with no rights. There would be no changes made. These things all had to have quite violent beginnings, actually, if you think about it. So this is actually quite nice, stopping a few people going to work. I think we’re at a good place and we need to go further and further, but people need to do it themselves. You can’t bully anyone into doing it, you have to attract people to do it.”

“It’s a bit like Question Time,” he laughs.

*

Everyone has a Beatles story. Here’s mine: I got the 1 compilation album for Christmas when I was nine and I played it over and over on my dad’s hi-fi in the living room, listening through headphones with my back pressed against the radiator. That anecdote is meaningless to anyone but me though, because you’ll have your own Beatles story. It might involve singing “Yellow Submarine” so loudly on the way home from a school trip that your geography teacher threatened to pull the bus over, or crying the first time you heard “Blackbird”. Paul Gascoigne’s full name is Paul John Gascoigne – not in honour of the disciples, but two lads from Liverpool. Liam Gallagher loves The Beatles so much he built a career on fronting what is essentially a Beatles tribute band.