Ordinary people dealing with traumatic shocks feature regularly in her award-winning body of work. But when her husband accused her of being an imposter in her own family, she wasevery bit as devastated as any of her characters. His words hung in the air as Abi struggled to make sense of them. “I know you are not who you say you are,” he told her. “Why do you have such an interest in my children?”

The man speaking was Jacob Krichefski, her partner of 18 years and devoted father of the couple’s two teenage children. The dramatic accusation followed a life-threatening reaction to an experimental drug for his MS which led doctors to put him in a medically-induced coma. When he woke up, Jacob, 49, started to experience hallucinations.

But it was the accompanying delusions that left Abi, 53, reeling. Jacob did not ­recognise her. Worse, he thought she was pretending to be Abi, the Bafta and Emmy award-winning playwright and screenwriter whose credits include The Iron Lady, Suffragette, The Hour and Brick Lane. Abi is also the creator and writer of popular BBC drama, The Split.

In that moment, all of their shared ­experiences – including his enduring support of her writing career – felt as if they had evaporated. “It was like a kind of a religious conversion he had gone through,” Abi tells me. “He was existing in a different way.”

At first, she says, it felt like a bad party game. “When someone denies your e­xistence they are denying your past. It was like that horrible disconnected feeling when someone tells you that they have fallen out of love with you. It was a seismic shift that left me literally shaking.

“If he wasn’t himself then I wasn’t myself. I realised how much of our past is woven into our present, how many times as a ­couple you refer back to ‘that birthday party’, ‘that holiday’, the births of our children…”

But all of the deep ­emotional riches of a long life together had apparently been erased from Jacob’s memory, including his awareness of who she was.

Now Abi has written her first book, This Is Not A Pity Memoir, the captivating and compelling story of the past four years that explores the delicate ic of long-term connection and what it reveals about our shared identity.

As the months passed, Abi continued to gently feed Jacob, a character actor, with bits of information and small affirmations about the past. “My hope was that he would believe me,” she says simply.

A medical assessment, carried out shortly after Jacob emerged from the coma, revealed the stark extent of the damage.

“While he has insight into the disturbing hallucinations, he does not waver on his belief that his partner is an imposter (Capgras syndrome),” it reported.

In passing, a doctor asked the Welsh-born writer, whose first TV writing credit was for ITV’s Peak Practice in 1998, if Jacob had ever expressed a desire to leave her, adding casually that in 80 per cent of Capgras Syndrome cases, the patient had wanted to end the relationship.

Reeling from that statistic, Abi suggested drily that, as far as she was aware, Jacob had not wanted to leave her before his illness. And she certainly didn’t want to leave him.

“Even if he didn’t know me, I knew this was my person whom I loved deeply. If someone you love is lost, you are going to do everything you can to help them find their way home,” she insists.

The day it all began was June 15, 2018, which had started out with an ongoing low-grade dispute at 7am about snoring, during the course of which Jacob mentioned having a searing headache. Seven hours later, Abi returned to their north London home and found him on the bathroom floor.

His lips were blue and dried blood was caked around his mouth. He had bitten his tongue. The only word he could say, repeatedly, was “what?”

After three days in hospital Jacob asked Abi, “What am I?”, and over the course of the next two weeks she watched him deteriorate as doctors attempted to find an explanation for his worsening seizures.

“By the end of June, two weeks in, he had started to unravel mentally and was having trouble with his basic functions and it was then that Jacob was put into the coma,” she recalls.

At last, Abi was given his diagnosis: Anti-NMDA receptor encephalitis is a type of brain inflammation that leads over time to delusions, seizures and hallucinations. It is now thought to have been a reaction to experimental medication for multiple sclerosis that Jacob was taking as part of a clinical trial.

The drug was withdrawn in March 2018, three months before his collapse and following a number of fatalities.

For the first few days after Jacob slowly awoke from his coma in January 2019, he was unable to speak due to the presence of a tracheotomy tube.

When it was removed, he began to communicate clearly. His vocabulary had emerged unscathed. But not his memories.

“Can you wait outside? Wait by the door please,” he asked Abi politely. “Me? You want me to wait outside?” she replied.

It was as if Jacob was addressing an over-attentive member of staff. A few days later it was Valentine’s Day. A nurse had arranged for Jacob to give Abi a red rose wrapped in cellophane. “Go on. Give your wife the rose, Jacob.” “She’s not my wife,” Jacob replied.

“Waking up from a coma and not remembering your partner is a cliché, to be scored through by any eagle-eyed editor worth their salt, in a red ballpoint pen,” writes Abi in her memoir.

Yet it was happening to her. And four months later, in May 2019, came more ­challenging news when Abi was diagnosed with an aggressive breast cancer.

“I felt like we were already running a ­marathon and having cancer felt like having a refrigerator strapped to your back while running. It was shocking and unreal,” she explains.

She was under so much stress that, in the first draft of her powerful memoir – which as its title suggests contains not an ounce of self-pity – she forgot to mention the cancer.

“My sister read it and pointed out that I’d overlooked the cancer diagnosis. I was so preoccupied, but there was no great humility in what I was doing,” she explains.

“I wasn’t being stoic, I was just trying to keep Jacob together with the support of our amazing family and friends.”

In the absence of Jacob’s support, she got through the cancer treatment, including a mastectomy, with the help of a brilliant oncologist.

“She looked like she headed up the UN, she was incredibly assured, so I outsourced it,” Abi says.

Having cancer gave Abi licence “finally” to lay on the sofa and watch a lot of “c**p TV”. “It also gave me time to reflect and process,” she adds.

She says that Jacob had been a 100 per cent hands-on father and a very robust and direct parent. He managed the minutiae of domestic life while she focused on being the main breadwinner.

“I fell into line with his philosophy with the children,” she explains. “I tried to be as transparent as I could. When I couldn’t cope I showed them. And when I could cope again I’d let them know. The children have found a level of resilience that still surprises me.”

And she constantly found ways to look for joy with Jesse, now 20, and Mabel, 18. “We would make up strange inventive meals, and got really into Love Island.” Still she continued with her loving nudges towards Jacob, hoping they would help their father to remember her.

“There is a muscle memory when you know someone so well. I would lightly touch his forearms, which I’ve always loved, and even though he didn’t know me, it was a way to try to help him find his way home.”

As the weeks passed, she began to see “ripples” of the person she knew, including occasional “firefly moments” when Jacob would stun his family with a witty insight or memory. A breakthrough in her own understanding came when Abi was getting him ready to see a consultant.

“I saw him leaning against the wall and staring at his reflection. I asked him ‘who’s that?’ and he didn’t know. I realised how ­terrifying it was for him. And, if he couldn’t recognise himself, how could I hope that he would recognise me?”

She doesn’t expect that Jacob’s recovery will be complete, but says the past few months have been something of a miracle. “We are reeling and recalibrating,” she says with delight. “We’ve got his wit, humour and intellect back. And his huge energy for life.”

Best of all, a year after emerging from his coma, Jacob now recognises the devoted woman who fought to find him again and who never stopped believing they could reconnect.

“It started in early Spring 2020, when he started to see similarities between me and a photo of us together on his iPad before his collapse.”

On June 21 last year, the couple were married. Abi pauses, then adds: “It is a gradual process but I feel that at last I’ve got my best friend back. He may be profoundly changed, but my favourite person is with me again.”

• This Is Not A Pity Memoir by Abi Morgan (John Murray Press, £14.99) is out now. For free UK delivery on orders over £12.99, call Express Bookshop on 01872 562310 or order via expressbookshop.com