With the possible exception of those of novelist Evelyn Waugh, the diaries of James Lees-Milne, published in 12 volumes between 1975 and 2005, have afforded me greater pleasure than any other exercise in the literary genre. (I still await, though, the chance to sample any of the nine volumes of Ego by the theatre critic James Agate, which a friendly reader of this column once advised might afford more enjoyment still.) In its gossipy, name-dropping upper-class tone Lees-Milne’s record of his activities — much of them concerned with his years of valuable work with the National Trust — bears obvious comparison to the diaries of his friend (and the subject of one of his biographies) Harold Nicolson. He was not just a friend, in fact, but one of his (many) male lovers, as I have now learned from Michael Bloch’s superbly written and enormously entertaining James Lees-Milne: The Life (John Murray, £25), though the information has possibly been available elsewhere.

What will certainly not have been known, I think, except among the circle of Lees-Milne’s closest friends, is that his lesbian gardener wife, Alvilde, also conducted a passionate affair with Nicolson’s lesbian gardener (and novelist) wife Vita Sackville-West, the portrait of whose marriage (in the words of the book title) was controversially revealed years ago by her son Nigel Nicolson.

Nothing in the Lees-Milnes’ marriage was stranger, perhaps, than the start of it. The wedding ceremony at Chelsea Register Office was attended by four witnesses — the Nicolsons, art writer James Pope-Hennessy and Alvilde’s cousin Angus Menzies — and the lunch party afterwards at their new flat in Thurloe Square was augmented by the composer Lennox Berkeley and the conservationist Rick Stewart Jones, both with their wives.

Mr Bloch writes: “It may have been some reassurance to Jim that all three husbands among the guests, as well as the two bachelors, were homosexual, three of the five being ex-lovers of himself [Nicolson, Pope-Hennessy and Stewart-Jones].”

The introduction of ‘Jim’ in this quotation might strike a jarring note with those unaware of the strong link between the writer and his subject. The two were great friends over two decades, from 1979, when Bloch was 25, to Lees-Milne’s death, aged 89, in December 1997.

Rather to his surprise, Bloch found himself nominated his friend’s literary executor, faced with the task of editing further diaries which he did with great skill in five volumes published between 2000 and 2005.

In the light of the gay tone to Lees-Milne’s life, one is naturally curious (well, a nosy parker like me is) about the nature of his relationship with young Bloch.

Just as Selina Hastings was in her admirable 2002 biography of Rosamond Lehmann (her new one, incidentally, on Somerset Maugham is another corker), Bloch found himself a character in the life he was writing. Having revealed all about Jim’s earlier pashes, he could hardly fail to be frank about his own relationship with him.

In fact, he tells us that his friendship, though very close, was entirely platonic. Perhaps Lees-Milne would have wished it no other way, for in great old age he had firmly put the gay life behind him — if that is not an unfortunate phrase in this context. Indeed, he had become something of a homophobe.

In 1995, he said he regarded homosexuality with “distaste”. Shortly before his death he confided to his diary: “Their mannerisms, their social contacts, their sharp little jokes are the same the world over. How is it that they do not recognise that they are artificial, shallow, slick, sophisticated, absurd?”

This seems a bit rich coming from one who spent his earlier life in one gay affair or another.

It would seem, though, that he sometimes found it easy to hide the truth about himself. Bloch cites an excellent example of this in the way Lees-Milne managed to conceal the fact that he came from a family ‘in trade’, which would have spelt social death had it been known at the time he began his climb.

In all respects, Bloch’s is an admirable and fair biography which, one hopes, might encourage many more readers to the delights to be found in those diaries. If nothing else it shows, in its account of his tempestuous life with Alvilde why it is perhaps not a good idea for a gay man to marry a woman (as we need to add these days).

The same lesson is contained in the aforementioned biography of Somerset Maugham whose appalling life with the former Syrie Wellcome makes for agonising but compelling reading.

A feature of Bloch's biography that particularly pleased me is his (partial) clearing up of a mystery surrounding an alleged visit his subject made in his youth to the Oxfordshire stately home of Rousham (above), which was built in Jacobean times and later redecorated and landscaped by William Kent. In his autobiography Another Self Lees-Milne describes how he saw its drunken tenant (unnamed but in fact Maurice Hastings, whose family owned The Architectural Review) take a riding crop to some of the Kneller and Reynolds portraits, and later aim a rifle at the private parts of the garden statues.

This destruction, he claimed, had been “a turning point in his life”, causing him to make a vow “that I would devote my energies and abilities, such as they were, to preserving the country houses of England”.

Aware of this passage, I found it very strange that in the 12th and final volume of his diaries, The Milk of Paradise, in which is described a birthday visit to Rousham in August 1997, he makes no mention of the episode. I raised the matter in this column at the time, marvelling that so formative an experience could have been overlooked.

Bloch’s judgment is that while the regrettable incident occurred, Lees-Milne was probably not present but heard about it from people who were. “Having heard about it, it is likely, given his propensities, that he would have relived the experience, imagining how he would have reacted had he been there. Should this have been the case, there is no reason why the experience should not have been a turning point in his life.”

Well, I think I see his point . . .