Since Claerwen James abandoned a promising career as a molecular biologist in 1999 and went to the Slade School of Fine Art, she has painted exquisitely wrought pictures of small children, who seem lost in a wistful world of their own. She denies they are intentionally autobiographical, but they do resonate with the sadness she felt as a child: “To some extent I see myself in most of them; yes, something is resonating there.”

Claerwen, 44, has never painted her own nine-year-old daughter, Maia, even though her daughter has asked her to. “Maia would be a terrific subject,” she says “but I can’t bear the idea. My paintings are melancholy and I would be afraid of creating a portrait that took Maia’s joyousness. I can’t do that to her, and it is not the way I want to see her. It is what emerges in my pictures because I think what I am painting is how hard life is and disappointment inevitable. I didn’t like being a child much.”

She is the daughter of humorist, author and poet Clive James and as a child pined for his time and attention, while he prioritised his work and was often away in a dizzy whirl of sociability and celebrity. The impact of what Clive, now 75, describes as his “faithlessness” to his family, undermined his marriage to Prue Shaw and Claerwen’s security. The parents lived in separate London flats during the working week and came together in the family home in Cambridge at weekends. Prue then kicked Clive out a few years ago when an eight-year clandestine affair with a model, in Australia, came to light.

It has been a tough emotional ride, but Claerwen smiles as she talks of how – since Clive almost died of renal failure five years ago, and is now chronically ill, frail, and having a mea culpa moment which has inspired a moving book of poetry Sentenced to Life – the family has come together in a way she could never have imagined.

When Claerwen walks me round to the Cambridge house Clive bought next door to hers, we sip tea on his tiny terrace overlooking the maple tree Claerwen planted for him when he was seriously ill last summer.

He talks of what his family endured because of his modus operandi as “an entirely self-centred, ambitious man who believed he was entitled to live as he wished. I have been faithless with my family, not valuing time spent with them. I wasn’t a hands-on Dad. Since becoming a parent, Claerwen has told me that I should have spent more time with her while she was growing up.”

Clive is surprised to find himself quite content living as he is now and with no prospect ever again of the razzmatazz of his younger years. He is the first to assure me that, for all his seeming vigour and ability to rattle off witticisms, his emphysema and cancer are chronic and life may well walk out on him at any moment.

While he admires Claerwen’s paintings hugely, he acknowledges: “There’s a great loneliness in some of her paintings and it is painful to realise I may be largely responsible for that.”

Claerwen says it is Maia, his adored grandchild, who has brought together the entire family, including Claerwen’s elder sister Lucinda, and Prue, to the extent that they all now live within 500 yards of each other and are in and out of each others’ homes and lives all the time.

She and her husband, Jonathan Grove, a scholar of medieval Icelandic literature, fostered then adopted Maia from the age of 18 months, after realising they could not have children of their own. “The family were united in delight at what this lively, life-giving person brought,” she says, as well as the way it seemed to make sense for the family to re-group and make the most of life in what Claerwen calls its “blessedly changed” form.

“Clive got attached to Maia instantly,” she says, “Watching them together drawing, talking about books or he helping her learn her part for a school play by speaking the other roles, brings to mind the good times that we did have.”

Clive remembers how he and his daughter found a shared view of the arts. He was reading Watership Down to Claerwen and saw her yawning. “This is an awful book,” he said and remembers Claerwen’s piping reply: “Yes, it’s awful.”

Claerwen wanted to work in a way that would allow her to collect her daughter from school and be at home with her afterwards. It also means she and Maia can be fluid in their visits to Clive. “Maia has a totally independent relationship with him based on the fact he has a bowl of humbugs in his kitchen. She announces ‘I’m just off to see Grunkle,’ as she calls Dad, and skims off next door. I tend to pop in for a few minutes every morning and he pops around most evenings and sits in my kitchen reading and he chats to Maia.”

Surprisingly, given the toxic upheaval of Clive’s infidelity, Prue and he are, in Claerwen’s words “completely involved with one another … it is approaching 50 years. It’s an awful lot of history to toss away and that I believe is a crucial part. Neither of them could find that again.”

Besides, Clive says chirpily that Claerwen has told him he is entitled to redemption, and her pleasure in having her father there in every sense these days, is palpable. “I think that as his life has contracted, he sees more clearly that he wants to stop and value what he has.”

There is pleasure too in sharing notes on their day’s work. Claerwen talks of the process of painting, he of writing the poetry that has been filling book after book, and seeking her opinion. Clive’s book, Sentenced to Life, is a record he will leave behind of his regrets. In Leçons de Ténèbres, he writes:

“All of my life I put my labour first.

I made my mark, but left no time between

The things achieved, so, at my heedless worst,

With no life, there was nothing I could mean.

But now I have slowed down. I breathe the air

As if there were not much more of it there.”

Claerwen sees him as being “at the top of his game, his poetry a far more thrilling and authentic use of his talents than earlier work. He has a very strong sense of this being the last chapter of his life – which, happily, seems to be a long chapter. But you hear the bell tolling: you know what’s coming and he is paying attention.”

So this is a time for savouring what is and living in the moment, says Claerwen: “I feel very blessed. Dad and I have a very rich relationship these days. It is absolutely lovely.”

• Claerwen James at Flowers Central, Cork Street, London W1, from 19 March, flowersgallery.com. Sentenced to Life by Clive James is published by Picador on 9 April