In 2017, Sally Bridges-Winslet died of cancer. She was 71. It was, her youngest daughter said, “like the north star just dropped out of the sky”.

It would have been even worse, says Kate Winslet today, had the family not pulled together. “I do have tremendous amounts of peace and acceptance around what happened because of how we were able to make it for her.”

Winslet’s eldest son, Joe, was then 13. “For him as a child, seeing that love poured into this moment was huge. And then he discovered through conversations with friends that that’s so rarely the case.”

Six years later, in 2023, Joe decided to turn the experience into a screenplay. A few drafts and some heavy-duty casting later and it’s a movie, starring Helen Mirren as dying matriarch June, Timothy Spall as her blithe husband, Bernie, plus Toni Collette (flighty hippy), Andrea Riseborough (organic fascist) and Johnny Flynn (oversensitive) as three of their children. Winslet plays the fourth (stressed exec); the film is also her directorial debut.

“However much I would try to separate my own personal experience from the experience we were having as this fictional family,” she says, “it was almost impossible. At times I almost felt like I was living out moments of my own mother’s passing that I never would have witnessed. So directing actors in a tender way without falling apart in the corner was definitely part of the challenge.”

The challenge was exacerbated by another she set herself: to make it as authentic as possible. Overhead boom mics were banned and crew banished once the cameras were rolling, the easier for the actors to avoid distraction. “That certainly made it all come flooding back. It felt very present. Even just the shape of the hospital room; the noises – oh God, that beep. When you’ve been through it, it does get you. That sense of monotony. The corridors. That it’s C17 for a Snickers in the vending machine.”

She smiles, clear-eyed and capable; friendly, professional and extremely keen the film (which she has also produced) not be misunderstood. Does cinema have a duty to be realistic about death? “It matters to me,” she says. “This is very much not the movie version of someone who is slipping away with cancer. And that was hard for Helen Mirren – not because she’s vain, but because it is emotionally difficult to be that broken-down and vulnerable.”

Goodbye June is a curious and winning mix of uplifting and unsparing: 60% Love Actually, 40% Michael Haneke’s Amour. Mirren does indeed look very ill, in bed and straining on the loo (the tumour has blocked her bowel). Spall has been issued with some strikingly horrible stunt legs, Bernie also not being in the best of health. Everyone looks like an actual flawed human being – unusual in a Netflix Christmas movie.

In one showdown with Riseborough, we watch as a blotch spreads across Winslet’s neck. “I really appreciate that you noticed that,” she says, “because when I get overwhelmed and stressy, my neck does go red.” The makeup artist flagged it; “Yeah, we’re totally leaving that in,” replied Winslet – just as she did when someone pointed out a bit of bumpy tum in her 2023 Lee Miller biopic.

“I’m infinitely more comfortable playing characters who don’t look perfect all the time, because I don’t understand that as a conceit. I want audiences to be able to see something of themselves, of their reality, in the stories playing out in front of them.”

* * *

The complication is that Goodbye June could be held up as an example of palliative best practice. For all its scrupulous accuracy regarding June’s condition – medical experts combed the script; it all feels totally kosher – her decline unfolds in an impeccably unhurried and compassionate hospital, to which June is rushed after a fall and allowed to remain for as long as she likes. Her family – so devoted their visits are put on a rota – deck out her en suite room with plants, tinsel, furniture and a fridge. She has morphine on tap and a specialist healthcare worker, Nurse Angel (Fisayo Akinade), who goes above and beyond.

“My initial thought was: could this be far-fetched?” says Akinade on the phone a few days later. But two palliative nurses – and his own mother, a carer – confirmed it wasn’t. “Not at all. One said: ‘The other week, we had a party in one room; I just put the family in there and closed the door.’”

Setting the film in Cheltenham, rather than London, was strategic, says Winslet, so the drama wouldn’t be overshadowed by chaos or overcrowding. “Everyone’s experience is going to be very different. But I really did find the endless warmth and outpouring of support from the palliative care team overwhelming.”

Later, Spall points out the film isn’t explicit about whether June’s care is fully NHS or partially private – “whether it’s a mixture of them both, you don’t know” – though the absence of that conversation means that I, at least, assumed the former.

For her own part, Winslet recently said that her mother’s condition necessitated moving her into a private ward at the very end of her life, about which the whole family were “horribly conflicted”. Spall uses both, he says: “It’s a bit of a lottery, which is the fault of the system. Some places are really organised and some are really struggling. If you’re lucky, you end up in a place like this one.”

“It was important,” says Winslet firmly, “to maintain June’s dignity and sense of pride as a woman.” At one point, her children discover June has already drawn up a care plan. “She had made her choices. Sticking to that mattered enormously. It felt very necessary not to deviate from honouring the agency she had in her own decline.”

There is some uncertainty among June’s children about when their mother realises she is never going home. Not for Winslet. “I think she knows exactly what’s happening. She knows that it’s coming and in those quiet moments when she’s alone, she is fearful.”

* * *

If Winslet the director has a proxy in Goodbye June, it’s not the character she plays, but June herself: the woman in the middle, orchestrating everybody while trying not to look too worried. “I wanted to let everyone be free to make mistakes,” she says of being on set, “and never let on if I was feeling the pressure of the time-crunch. Because if you’ve only got 35 days, and Helen Mirren for 16 of those days, and seven children, you have to make your days.”

She managed this by being “very, very good at being able to see everyone and assess what they need. I’d be talking to Tim one minute and then just revolving my body and engaging with Helen in a completely different way about the same exact scene. I found that really fascinating, knowing how to flip and adapt, and being open to how different and sometimes odd people can be in the greatest of ways.

“I can count on the fingers of one hand – or less, frankly – the tricky experiences I’ve had with actors across 33 years. You have to be totally non-judgmental and embrace whatever that person brings into the room.”

Spall backs this up. He first worked with Winslet in 1996 and says he always knew she would be a good director. Still, the atmosphere on Goodbye June was “exceptional, considering when you look at the lineup, you go: ‘OK, fucking hell, this could go either way.’ But instantly there was this warmth and kindness. She’s worked with some of the best directors in the world, had good and bad experiences, and is ultra-intelligent, ultra-open.”

Especially with the children – whose scenes are notably unforced and charming. “You get so many directors who are afraid of kids and let the handler deal with their stuff,” says Spall. Winslet, however, would set up shots with a baby on one arm, a toddler at her side, playing with another one, chatting to actors all the while. “She’s a mum, you know; got three kids of her own. Knows what she’s doing.”

It is too crass, I ask her, to suggest female directors do things differently? “No,” says Winslet. “Female directors do operate in a different way. I really think so, just because of our sensibility. Typically, female directors are mothers and the amount of mothering that we do in our own lives automatically transfers because you want to look after everyone. It’s just an instinct. This is not to say women are better than men. I would never ever say that. But it is different.”

* * *

I speak to Winslet solo in a Soho hotel room. Shortly after she leaves, Riseborough and Collette come in to pay tribute to her and talk about death. Of all the cast, Collette seems happiest to engage with that tricky thing: the film’s potential place in the assisted dying debate.

“I think society in general likes to manipulate and control,” she says, forthright and smiley. “And if you can’t give someone the privilege of letting go of their experience on Earth with any kind of grace and space, then that’s really fucking shit, isn’t it? To be able to do it in the way that they want.”

“I’m a Scorpio,” she continues. “I have a very active, passionate, spiritual life and I think the problem with humanity is that we feel so disconnected from everything else. Not just people, but from nature. We are nature. I think the soul does live for ever and this is a transient experience. None of us know, and that’s why it’s fucking marvellous.”

Riseborough nods. The two women are on the same page; one just reads it out a bit more. “I used to be very, very angry,” says Collette, “about the fact that our very existence is a mystery. It took a lot of time to work through it. Now I just think it’s beautiful.”

After a screening of the film the previous night, says Collette, she cried thinking about people spending Christmas alone: “It breaks my heart a little bit.” She trails off, then slaps her knee in mock cheer: “But if they’ve got Netflix, they’ve got us!”

“It’s very healing to see people come together over death,” says Riseborough. “It may sound morbid …”

“It’s not morbid!” says Collette. “It’s part of life. And it can be a celebration.”

* * *

I speak to Spall in the same room, too, alongside tea and Johnny Flynn. Spall merrily reminds us he almost died, aged 39, of leukaemia, so he’s had “a peek over the precipice” and has a “vested interest” in demystifying the whole business.

“Shitting and sex and death: all are taboo and all happen all the time, but we hardly ever talk about them properly,” he says. “When someone dies, there’s a ring on the bell and the milkman wants his money. That’s what happened when my dad died.”

Both men happily bat back and forth what seem to be the film’s most overt nods to religion: scenes in a chapel; God’s-eye camerawork; the nurse called Angel; a nativity play just as things get really critical. Dying, they agree, makes such reflection inevitable.

“There’s an old saying,” says Spall. “‘There are no atheists in a foxhole.’ If you’re at war and about to die, you’re praying to something.” For his part, he reads and thinks constantly about “eschatological matters”. Names like Meister Eckhart, Rumi and Richard Rohr tumble from him. In 2023, he mounted an exhibition of his canvases of angels in anguish.

Flynn listens sympathetically. Spall paints; Flynn writes and records music – songs rooted in English folklore and rural mysticism. “In Christian liturgy there’s this service I love called compline,” he says, “which is basically about getting ready for bed. It’s really short, but it has a sense of like: right, I’ve got from here to there.”

Contemplation is always helpful, however final the event it marks. “And it always boggles me, the absence of meaningful spiritual conversation around Christmas. So it is really nice to have a small sense of that energy and meditation. In society today, we’re not encouraged towards asking questions in the face of death, because it’s not in the interests of the powers that be that we really think about what’s going on in terms of our purpose on the planet.”

June hopes to be reincarnated as snow, or to live on through the stories told by others. Flynn’s father died when he was 18; he now sings to his children a lullaby his father wrote. “So, in a way, my dad is still singing my kids to sleep, even though they never met him. And they have this really strong sense of him.”

Spall is moved – and heartened. “Whenever you are in a strain of memory, you are immortal, because you’re still living in other people.” And there’s more, he thinks; something deeper, something spookier: “Just at the moment my daughter was born, a tiny little thing, I saw everybody I knew in my family flash right past her face, like a kaleidoscope.”

Goodbye June is a film born from a similar impulse: to keep alive those who have gone before by sharing their memory, and hoping it helps others. To encourage ghosts, not exorcise them.

“You learn to live with the changing shape of grief,” says Winslet. “And whether you like it or not, you might see signs of that person in places and actually feel their physical presence. Particularly at times of year when you all would come together, like Christmas. In those moments, I certainly feel my mum is still very much around.”

• Goodbye June is in cinemas from 12 December and on Netflix from 24 December