This month Frances Partridge can be observed in both reality and fiction. Living in London in the 1990s, she is au fait with contemporary life and recently travelled to France by the Channel tunnel. But she can also remember seeing from a nursery window the commotion when a bushorse fell down in the Tottenham Court Road.

Now in her ninety-sixth year, she has lived to see her earlier self portrayed by another on screen in Christopher Hampton’s Carrington. Translated into the medium of film, facts take on a different slant, reality shading into myth. The film celebrates the love of a painter, Dora Carrington (played by Emma Thompson), for Lytton Strachey (Jonathan Pryce), the man who undid Victorian certainties with his ironically titled Eminent Victorians.

At Tidmarsh Mill and then Ham Spray, in Wiltshire, Carrington kept house for Lytton, cherishing him with a creativity that extended beyond her painting and into their daily lives. She also accepted his homosexuality, even going so far as to marry Ralph Partridge in order to keep near at hand the man on whom Lytton had come to depend. When the marriage broke down and Ralph took up with Frances Marshall (as she then was), Lytton, fearing that his menage was falling apart, arranged to see this young woman in London. This meeting, both in life and in the film, was pivotal. To Lytton’s relief, Frances had no intention of destroying the circumstances sustaining this complex tangle of relationships.

“What I admired a lot about Lytton,” Frances Partridge today recollects, “was his integrity. I think he stuck up for what he believed in.” One ambition which Strachey shared with his Bloomsbury friends was to banish the fog of superstition in people’s lives, to replace unreason with reason. The young Frances Marshall, who married Ralph Partridge after Carrington’s death, shared this concern. She had gone up to Newnham College, Cambridge, in 1918 and for Part 2 of her tripos opted to read moral sciences - philosophy, psychology, logic and ethics. These subjects left her, she now thinks, “wanting a realistic attitude to life, with a passion for truth and an interest in the way people’s minds work”.

The Strachey family has in fact dogged her life from the start. Her elder sister, Judy, married one of Lytton’s nephews, while at school Frances became best of friends with his niece, Julia Strachey. When Frances went up to Newnham the Principal was Lytton’s sister, Pernel Strachey. In those days it was forbidden to have a man in your room without a chaperone, so Frances invented a “Mrs Kenyon”. “And how is Mrs Kenyon?” Pernel would ask, a little archly, knowing all too well that this lady lacked substance.

“There was a revolution during my time,” Frances Partridge recalls with amusement. Owing to the fact that rich girls, who could afford sitting rooms as well as a bedroom, were allowed male visitors, the rest felt hard done by and began to protest. “A meeting was called with the authorities and a brave girl got up. ‘Is it the bed you’re afraid of?’ she asked.”

In the wake of Lytton’s death and Carrington’s suicide, Ralph and Frances Partridge returned to live at Ham Spray, surrounded by many mementos of a former life. Frances was always keen to apply her mind to a literary task and at Lytton’s behest had worked with Ralph on an unabridged edition of the Greville Memoirs. While bringing up her son, Burgo, she agreed to index James Strachey’s translation of Freud for the Standard Edition which runs to 22 volumes. “I sometimes still feel as if I’m the only person who’s read the whole of Freud,” she laughs. “I think Freud was an amazing man, much more inventive than most people. The problem was his followers became rather religious about him.”

The religious attitude of mind, whether it attaches itself to Freud or Christianity, is something she distrusts. Having lost her faith at the age of 11, she has never, even in the worst of crises, sought to revive it. Instead she has placed her trust in what human consciousness can achieve. “What magnificent sanity,” she wrote in her diary after listening to a Handel fugue. “In a few bars he convinced me, against all reason, of life being worth living.”

This passage was written during the difficult period that followed her husband’s death in 1960. After this she uprooted herself from Ham Spray and moved to a flat in Belgravia. In 1978, after having translated or indexed other people’s books, she suddenly published her own, finding material to do so in her diaries. A Pacifist’s War covered the war years (“war is a special form of non-reason”, she argues).

It contrasted her intense pleasure in her circumscribed private world with the bleakness and horror of war. It also demonstrated her belief that the best defence against anxiety is knowledge. She wanted, she said, to be “as intensely conscious as possible . . . always reaching to something in my surroundings . . . nothing must be passively accepted”.

Having become an author at the age of 78, she went on to produce a stream of publications: Memories, an account of her early years, a portrait of her friend Julia Strachey, Friends in Focus, based on her photograph albums, and four other volumes of her diaries. Her readers became familiar with the characters, many of the Bloomsbury originals, descendants or fringe admirers, who enter these books. But the rationalism and intellectual honesty left her readers unprepared for the searing despair she confronted in her diaries after the death of her husband and again, three years later, of her only son, from a heart attack at the age of 28.

After the latter event she wrote in her diary: “I have utterly lost heart: I want no more of this cruel life.” However, her ability to articulate awful feelings created an outlet. Even at her most despairing she was able to remark in her diary on the egotism of suffering. Nor did her inner struggle ever occlude her responsiveness to the world around her. She loves reading, music, argumentative talk and is a keen observer of people and places. After observing the arbitrary groupings of people, dogs and activities in Hyde Park on a late autumnal day, she found it impossible not to feel “a sort of exhilaration - an utterly irrational sense that the stuff of life is good”.

This steady turning of her private diaries into a public gift has left her much in demand, as a book reviewer for The Spectator and elsewhere, and as a star on the literary circuit. At the Charleston Festival this summer she held her mixed audience enthralled as she countered VE celebrations with her view on pacifism, while her views on the Carrington film can be found in the current issue of the magazine Modern Painters. Though overall she admired the film, she regretted the use of a stockbroker-type residence for Ham Spray instead of the Georgian original. Later this month a preface by her will appear in Jan Marsh’s Women of Bloomsbury. At a recent gala event at the Barbican to celebrate the release of the film and the opening in its Gallery of a Carrington exhibition, she could hardly move for the persistent knot of people anxious to talk to her.

Though never a member of what Leonard Woolf termed “old” Bloomsbury, its original core, she was very close to some of the central figures and became one of the later dramatis personae. Paintings by Carrington and other Bloomsbury artists still hang on her walls, (Carrington’s portrait of Strachey is at present on loan to the Barbican) demonstrating loyalty to her past, for she upholds the importance Bloomsbury attached to friendship. In her diaries she observes her friends with love and criticism, noting, for example, the critic Raymond Mortimer’s benign sociability as well as his childish petulance, and recording also the exasperation Julia Strachey sometimes caused her. But she also insists that E M Forster’s remark is profoundly true: “Kindness, more kindness, and even after that more kindness, I assure you it’s the only hope.”

On first entering Bloomsbury in the 1920s she caught the admiration of many. Clive Bell praised her “gravely humorous conversation and airily competent mind”. He also remarked that her legs were the prettiest in London. Certainly she cast a critical eye over the actress playing her younger self. “I don’t think I would have worn a dress like that,” she remarked of one publicity photo for the film. In recent years she seems to have become increasingly stylish and unconventional in her dress. When Issey Miyake decided to design clothes for the elderly in the 1980s she agreed to model some. Despite the vulnerablity brought on by age she still cuts a dashing figure at public occasions.

Recently on Radio 4 Bertrand Russell’s niece harangued Bloomsbury for the destructive effect its legacy has had on young people today. In her view its libertarian views and lack of respect for conventional rules have led to anti-social self-gratification. Yet if one turns to the letters and biographies that have been published, or to France Partridge’s diaries, what is striking is the careful, attentive analysis of relationships and the moral austerity that clings to their view of life.

Bloomsbury Women: Distinct Figures in Life and Art by Jan Marsh, with a foreword by Frances Partridge will be published later this month (Pavilion Pounds 17.99) The exhibition Dora Carrington 1893-1932 is at the Barbican Centre, London EC2 until December 10.