There is a restaurant on Gerrard Street in London’s Chinatown in which an observant diner can still detect marks on the wood panelling where bookshelves once lined the walls. These are the former premises of the bookshop Birrell & Garnett. It says something about the decorative standards in these parts that the restaurant dates from the 1970s. The fabled bookshop’s heyday was a full half-century earlier, when Gerrard Street, with its mix of cheap tailors, ‘foreign’ restaurants, coffee shops, glamour studios and brothels, belonged to Soho. It was a suitably louche choice of place for Francis Birrell and David Garnett – Frankie and Bunny to their Bloomsbury intimates – to open a shop in 1920.

Bunny is the better remembered of the two. He had huge success with his first serious novel, Lady into Fox (1922), and his Aspects of Love (1955) was turned into a musical by Andrew Lloyd Webber. He is immortalised in Bloomsbury lore for having married the much younger Angelica Bell, the daughter of his former lover Duncan Grant. A classic bugger’s muddle, as that generation used to say.

But what of Frankie? Francis Frederick Locker Birrell was the son of the spectacularly useless Liberal politician Augustine Birrell. His mother had previously been married to Tennyson’s son. In October 1909 he met Lytton Strachey; by Christmas he was in the Bloomsbury circle and visiting the Stephens in Fitzroy Square. Memoirs of the period paint him as a charming, absent-minded scruff, smoking cigarettes and fiddling with his flies while attempting to peddle English and French literature and the slim volumes published by his chums at the Hogarth Press.

As tolerant of Frankie’s eccentricities as they may have been, his customers would perhaps have been surprised by the contents of an unprepossessing manuscript notebook with the cover title ‘A few remarks on life as it really is!’ Brought to me a couple of years ago by a book runner, I didn’t hold high hopes for it. Even the greatest writer’s notebooks can be disappointing for the rare-book dealer, usually containing little more than long-expired phone numbers or queries to be addressed to accountants. The only thing to do was to decipher his spindly hand and read.

Frankie began his notebook at Lausanne on 4 September 1911, in his twenty-third year, and he evidently made additions and revisions to it over the next few years. He explains that he intends to entrust the notebook to a friend. It will be returned to him if and when he has children, so that he can review the advice only his younger self can give to his offspring, as ‘I feel that parental stupidity will be eternal.’

Foreseeing having to tell his imaginary son about the perils of school (where he ‘will probably be buggered when he is small & bugger others when he is big’) sets Frankie recalling his own education at Eton and King’s College, Cambridge. His reminiscences read like the blueprint for an Alan Hollinghurst novel. He starts with his cousin Aubrey Tennyson: ‘I very much wanted to bugger him (one day lust came on so strong that I thought I should have to leave Chapel).’ He describes showers with a fellow student who ‘would give himself an erection & was gratified by my frank admiration of the size of his genital organs’. And so on and on, with unembarrassed candour.

Poor Frankie’s sense of his own ugliness led him to be grateful for any crumb that fell his way: ‘I don’t think I shall ever forget my feelings my first year at Cambridge when I discovered W D Evans wanted to bugger me. I looked on this as an entirely unselfish action on his part. I thought it so kind of him that while disliking his mind & being repulsed by his body, I very nearly fell in love with him. If he had been the slightest bit nicer, I am certain I should have done.’

He credits any subsequent improvement in his character to his pure love for Gerald Shove, one of the Cambridge Apostles and later an eminent economist. (Shove married the poet Fredegond Maitland in 1915.) But Frankie also fooled around with the leading figure among the Apostles, John Maynard Keynes.

I copulated with Maynard for 2 reasons: a) Out of a spirit of adventure; b) Because it pleased me to think I would copulate with a person I wasn’t in love with & so score off Gerald. The whole affair was frivolous. Maynard knew I was not in love with him &, as regards me, his was a ‘cock & ball’ affair, to use a phrase of his own, as opposed to ‘a hand & heart’. I have not in the least regretted the experiment.

Frankie ends his notebook with a poem, ‘A Rapture from King’s’, in which he mentions Michael Haslam (‘gambolling in the dew’), the civil servant Patrick John Chester Purves (‘tripping wantonly’), the classicist John Tresidder Sheppard (‘round whose childish bed/The fairies all their daintiest gifts did spread’) and Keynes (‘A shrewd philosopher, a courteous friend’). The poem uses the word ‘gay’ in its modern sense.

In its matter-of-fact autobiographical frankness, Frankie’s account is quintessentially Bloomsbury. Some of the sexual behaviour of that circle and generation now revolts us (Eric Gill’s especially so), but writing only a few years after the Wilde trial, Frankie is entirely cheerful and guiltless. As a point of comparison, I opened a copy of Frankie’s A Letter from a Black Sheep, a neglected pamphlet published by the Hogarth Press in 1932. Here Frankie employs the same confessional format, but without, as Alec Guinness’s parson in Kind Hearts and Coronets would say, any of the concomitant crudities of the period.

Frankie in the end didn’t marry, and so the notebook was never returned to him. The friend to whom he had chosen to entrust it, the physiologist and nutritionist V H Mottram, was a research fellow at Cambridge when Frankie was there. At university Mottram was perturbed by his own homosexual leanings, which he suppressed by a course of psychoanalysis; he later married and fathered three sons. Mottram passed on Frankie’s notebook to Arthur Waley, the translator of Chinese and Japanese literature and another King’s man. The notebook was found among Waley’s papers long after his death in 1966. As with many such archives, the bulk of Waley’s papers are now in an American university. This notebook was apparently discarded as irrelevant to the collection.

The Birrell & Garnett partnership was broken in 1924 when, in order to concentrate on writing, Bunny sold his share of the business to the keen young bibliophile Graham Pollard. Frankie did not fully recover from an operation on a brain tumour in 1933; he died in January 1935. We recently sold his candid notebook to a private collector for a high four-figure sum.