The third volume of TS Eliot's letters covers 1926 and 1927, years in which the poet described his personal life as being "like a bad Russian novel". The behaviour of his wife Vivien grew increasingly erratic, and her paranoid delusions led to her being hospitalised at the Sanatorium de la Malmaison in Paris. One of the first letters in the book is from Vivien to her husband. In a frenzy of repetitions, underlinings and italics, she claims to have uncovered a plot, orchestrated by her psychiatrist, to drive her into having an affair with a masseur: "The net is being drawn bit by bit, so stealthily, so cunningly round me " In other letters she feels persecuted by Eliot's family, and even by Eliot himself: she tells a friend that she sometimes thinks he is "mad or else that he is most frightfully & subtly wicked and dangerous. That he is a terrible menace."

In order to escape from the turmoil of his personal life, Eliot buried himself in work. The staggering amount of correspondence generated by editing the Criterion is what swells this volume to such a size. Eliot had mixed feelings about being an editor. We can hear both despair and residual pride in his financial self-sufficiency when he writes to Ezra Pound: "All reviews are worse than useless and my only excuse is that I derive the larger part of my income from this source." Elsewhere, he notes with astonishing self-awareness the emotional impulse behind his work ethic: "To have people depend on you is perhaps the most substantial and solid human relationship, in general, that there is; for you can depend on people's dependence more than on their affection."

Overworked he may have been, but as Eliot explains in a letter to a young poet: "it is not merely the time you spend with pen and paper but is as much, or more in fact, that you always keep a corner of your mind working on poetry, more or less unconsciously." The fruits of Eliot's unconscious labour in these years were strange indeed. The verse drama Sweeney Agonistes and the dramatic monologue "Journey of the Magi" seem worlds apart, but the letters show that both developed out of Eliot's understanding of his chaotic life in religious terms. The surreal burlesque of Sweeney Agonistes, with its insistent repetitions and melodramatic urgency, is eerily reminiscent of some of Vivien's letters; but, more intriguingly, in a letter to his brother, Eliot incorporates its refrain ("Birth, and copulation, and death") into a complaint about their family's Unitarian religion: "Unitarianism is a bad preparation for brass tacks like birth, copulation, death, hell, heaven and insanity: they all fall within the classification of Bad Form." The often-anthologised "Journey of the Magi" is very different, being a calm, measured work of Christian symbolism; but Eliot admitted that it too emerged from his tumultuous life: "I wrote it in three quarters of an hour after church time and before lunch one Sunday morning, with the assistance of half a bottle of Booth's gin."

Valerie Eliot and John Haffenden faced considerable challenges in editing this volume. While there is a great mass of business correspondence, there are no letters from Eliot to Vivien. (Presumably, Eliot destroyed them; the editors don't say.) Including a selection of Vivien's letters allows insights into the Eliots' unhappy marriage, but it is an inevitably partial account and the editors' policy on which letters they chose is not entirely clear. When Vivien is hospitalised for a second time at Malmaison in 1927, she all but disappears from this volume. Eliot claims that she wrote to him twice a week at this time, but none of those letters appear here.

Another significant absence is any correspondence between Eliot and Emily Hale, the woman he loved for most of his life. The reasons for this are explained in the preface to the first volume: Hale gave her collection of Eliot's letters to Princeton University Library, where they will remain under embargo until 2020. These gaps leave us with a sketchy understanding of Eliot's emotional life, which is particularly unfortunate since his least sympathetic side is so well documented. Many of his letters to Bonamy Dobrée make for painful reading, consisting as they do of racist doggerel about an invented tribe called the Bolovians and a "Bastard Jew (named Benny)". Eliot's more offhand antisemitism is equally dismaying: Laura Riding's poetry exhibits "a variety of Jewish cleverness", while Samuel Roth's unscrupulous exploitation of copyright loopholes is an example of "New York Jewish piracy".

A more textured portrait of Eliot emerges in the meticulous footnotes that Haffenden and Eliot provide. The editors draw on an array of secondary sources in order to describe key events, such as Eliot's baptism and confirmation into the Anglican church, or his taking up British citizenship. The footnotes also contain many odd, touching details: on one occasion, Eliot takes Geoffrey Faber to see a boxing match at the Albert Hall; on another, he offers to buy a cake for Virginia Woolf's visit, but she replies "No cake needed. A penny bun is what I like most of anything in the world." Such details serve to humanise Eliot, who otherwise remains a distant figure.

Eliot had dozens of correspondents but few confidants, and apart from some candid letters to his brother, and one moving expression of love and gratitude to his mother, we hear frustratingly little from the private man. Not that he would have minded: "I don't like reading other people's private correspondence in print, and I do not want other people to read mine." In a sense, this volume honours that wish, since it consists for the most part of correspondence in which Eliot cultivated his public mask. The mask is yet to slip.

 Paul Batchelor's The Sinking Road is published by Bloodaxe.

TS Eliot maintained that "the more perfect the artist, the more completely separate in him will be the man who suffers and the mind which creates". The black box and the air crash. Objectivity and a torment of twisted metal. But there are many differing degrees of separation, and the story told by this latest volume of Eliot letters is the separation of the dapper man of letters from the agonised individual, whose paranoid, delusional wife, Vivienne, is under suicide watch at the Malmaison sanatorium in Paris.

We glimpse Eliot watching the boxing from Lady Rothmere's box at the Albert Hall. We see him dispatch Emerson ("set up a new standard of Ignorance in America") and Santayana ("a poseur"). He puts the boot into Bertrand Russell: "All the reasons you advance [against Christianity] were familiar to me, I think, at the age of six or eight Why don't you stick to mathematics?" He drinks too much of Harold Monro's excellent whisky. He is learning to drive. He gossips with Virginia Woolf and drinks six cups of tea. They play the gramophone. He teaches her "what little I know about the Grizzly Bear, or the Chicken Strut". He watches Ernie Lotinga, "the greatest living British histrionic Artist, in the purest tradition of British obscenity". He sings "too much" at a Criterion dinner in a private room. And all the time, Vivienne is going unsteadily mad: "I am in great trouble, do not know what to do. In great fear."

This latest volume (edited by Valerie Eliot and John Haffenden with unblinking attentiveness to the reader's every need) covers the years 1926 and 1927. In this period, Eliot falls to his knees in St Peter's, Rome, to the astonishment of his companions; is privately received into the Church of England; becomes a British citizen; and fails to get into All Souls because some fellows ("sons of the manse") denounce his poetry as "obscene and blasphemous". He acts as executor of his father-in-law's will and negotiates probate. As editor of the Criterion, he solicits reviews, manages an enormous correspondence, soothes prickly contributors and tries to make the magazine a going concern. (The sales average between 700 and 800 copies per issue.) By the end of 1927, his backer, Lady Rothermere, has pulled out, but the magazine manages to struggle on: her gold-plated stupidity and her brisk, cheerful tactlessness are amply illustrated. This is one narrative, the story of Eliot the exceptional juggler, sorting and sifting, capable of coping with a hail-storm of commitments.

The other, darker story shows Eliot standing in a shit-storm, buffeted and barely upright. Humbert Wolfe: "I can't understand how a body so thin and white goes on living." Aldous Huxley: "I lunched with Tom who looked terribly grey-green, drank no less than five gins with his meal." Eliot himself was grimly bemused: "It often seems to me very bizarre that a person of my [Unitarian] antecedents should have had a life like a bad Russian novel."

Now and then, Vivienne emerges from her troubled sense of persecution, the hallucinatory voices swarming in her head. Eliot's niece Theodora has tea with her in Paris and spiritedly opposes the family tendency to deplore Eliot's disastrous marriage: "Aunt Vivien [sic] whom I like better every time I see her. She is a dear & so absolutely wide awake & very bright."

Theodora thinks Eliot may have gained from the marriage. (This is bound to be true, considered artistically. In Ulysses, Stephen Dedalus says: "A man of genius makes no mistakes. His errors are volitional and are the portals of discovery." This is Eliot's version in 1916: "I have lived through material for a score of long poems in the last six months." All good writers know that even disaster, especially disaster, is material.)

More often, though, Vivienne was incapable of separating her troubled personality from her social self. Her spasmodic appearances were tainted by her inner turmoil. Included here is Osbert Sitwell's vivid, unforgettable, previously unpublished account of a wary, tense evening chez Eliot, with James Joyce and Nora, Geoffrey Faber and his wife, Enid, as guests. The atmosphere is one of dutiful jollity. Vivienne is understudying the role of Banquo. Enid Faber tells her the evening has been "lovely". "Vivien looked at her mournfully, and replied, 'Well, it may have been lovely for you, but it's been dreadful for me.' Mrs Faber, rather at a loss, rapped out at her, 'Nonsense, Vivien, you know it's been a triumph.' Vivien repeated in desolate tones, '"A triumph"!... Look at Tom's face!'"

Given Vivienne's baleful behaviour, her affair with Russell, her general impossibility, it is an unsurprising surprise that one of Eliot's letters confesses unequivocally to adultery. He is pre-empting a charge of excessive puritanism: "I remember also minor pleasures of drunkenness and adultery"

There are two controversial things. One is the epic of facetiousness about "a race of comic Negroes wearing bowler hats"  including some racist, obscene poems that easily offended readers will find offensive. I think it is allowable comic licence  knowingly transgressive like Lotinga, whom Eliot was taken to see by his Jewish friend Jack Isaacs. One of many examples of Eliot's warmth to Jews: "A few weeks ago I saw Horace Kallen, Shef's Jewish friend, whom I like" In 1951, we learn, Eliot writes a supportive reference for an Italian Jew, Leon Vivante, who left Italy "after the promulgation of the anti-Semitic legislation". Ah yes, antisemitism. In a letter about "the German Jew, Lion Feuchtwanger", Eliot writes: "I simply put it to you whether the appearance of a new book by the same person makes necessary a consideration of his work. I am always prejudiced against such people, but I have never read anything by this man." Eliot's adversaries will read this as an admission of antisemitism. Others will read it as a prejudice against literary incontinence, against polyphiloprogenitiveness.