Lucian Freud was never short of confidence. In the 1990s he painted a small head of an especially rich individual and demanded a stunning £800,000 for it. The sitter demurred. In 2002 this very obvious likeness was displayed at a big Freud exhibition at Tate Britain with the title Head of a Man. It seemed like a snub, but Freud’s titles were unpredictable: sometimes a sitter would be named but sometimes he or she remained anonymous, even in the case of another rich individual, the industrialist and art collector Heini Thyssen, who had bought both Freud’s likenesses of him and other paintings by the artist as well.

Thyssen did, however, purchase a kind of immortality. Freud’s portraits of him form part of one of the artist’s most interesting exploitations of an Old Master, in this case Antoine Watteau’s Pierrot Content, which Thyssen owned and which Freud made a careful drawing of. Part of Watteau’s painting appears in the background of Portrait of a Man (1981–2), in which Thyssen’s head blocks out the figure of the pierrot, hinting at an identification of one with the other.

Watteau’s painting is also referred to in Freud’s study of Thyssen seated, Man in a Chair (1983–5), where the sitter appears in an uncompromising modern suit and tie but adopts the melancholic pose of Watteau’s ultimate sad clown. The work is full of psychological insight and genuinely, as many great paintings are, set within a larger historical context that amplifies its meaning. Large Interior W11 of 1981–3, featuring Freud’s children and lovers, is another variation on the Watteau, though far more loose and almost whimsical – ‘a slight bit of role-playing’, as Freud remarked.

You will learn little or nothing about this important Watteau-related group of works in the sparse text included in what will inevitably be called ‘these lavishly illustrated volumes’. There are, though, plenty of entertaining titbits about Freud’s private life and, especially, the identities of his sitters. And a right old mixture they were: children, lovers, bookies, models, wives, husbands, a fat gay performance artist and an even fatter benefits supervisor, all dropping their clothes, so that, in his later works especially, mountains of flesh slop about before us, to Freud’s, if not always our, great satisfaction.

Although at the age of seventeen he went off to study at the grandly titled East Anglian School of Painting and Drawing (in practice an old house in Dedham belonging to Cedric Morris and his lover Arthur Lett-Haines), Freud was essentially self-taught, since the school believed that artists ought simply to discover themselves without formal instruction. It meant that, in the absence of any solid technical foundation, Freud’s painting, like that of another famous autodidact, his friend Francis Bacon, was hit and miss. He was acutely aware of that, and by all accounts worked himself into a state of great tension when painting, once in his anxiety managing to stab his thigh with a paintbrush, drawing blood.

Gambling, with the adrenaline rush it provided, was linked in Freud’s mind with the edgy unpredictability of painting. He was able to command vast sums from the 1980s onwards, but the amount of money he ran through was equally enormous. Martin Gayford describes this aspect of Freud’s personality very well here. He was not a good gambler, if such a thing even exists, and his endless losings were assiduously collected, through a mixture of dire threats and oily cajoling, by the bookies who, weirdly, often became Freud’s close associates. Several of them even became sitters, not least because Freud resorted to that well-known stratagem of impecunious painters, painting a portrait for someone in return for being released from a debt. In Freud’s case, at least, the bookies could reckon themselves amply repaid.

The works of self-taught artists who become successful raise peculiar questions. For example, it is tempting to argue that, as Bacon gradually became more proficient, his painting became less, not more, interesting, verging on the slick, even mechanical. Is the same true of Freud? It is a tough one. He himself, we are told, felt that by the 1990s his painting had changed, believing that it was ‘just more accomplished’. My own sense is that the later paintings lack the tension that distinguishes his work of the 1980s, perhaps his best decade. A real awkwardness of technique was always part of Freud’s distinctive appeal, and I think I detect a striving to retain that peculiarity at a point in his career when his technical mastery had increased to such a degree that he may have found it uncomfortable.

Gayford knows much more about Freud than most. He sat for him, a taxing exercise that lasted seven months, and has written illuminatingly about the experience in Man with a Blue Scarf. In these volumes he is always informative, but the tone is unfortunately reminiscent of those pointless interviews with contemporary artists that one hears on The Today Programme: ‘Tell us why you are so great.’ There is nothing remotely critical in these books about either the art or the man. It is all a little relentless and one-dimensional. By the time we reach ‘The Nineties’ (the volumes are organised by decade) the prose shows signs of strain and becomes positively fulsome: ‘the sitter in Portrait on a Red Sofa is static on a piece of furniture, but positioned like an angel by Michelangelo, flying through space.’ Which angel by Michelangelo might that be? Strained comparison with an Old Master is a ploy adopted by many an art critic attempting to whip up interest in a modern artist. Freud does not need it.

There are awkward questions to be asked about the later pictures. Are all those uphill floorboards really successful, or are they distractingly bad? Are the tiny oils of the Queen and Jerry Hall just clumsy? And did his use of electric light and his habit of painting by night in the later years simply rob, to little advantage, his pictures of the play of daylight that he captured in the 1960s in such masterpieces as Large Interior, Paddington? Later on, Freud could still do daylight, as we can see in Large Interior, Notting Hill (1998), but I am not convinced when Gayford claims that the boards in Lying by the Rags (1989–90) are ‘amazingly dynamic: the light catches the knots and grain in the wood’. No, they aren’t, and no, it doesn’t. That’s the trouble.

Like others of its kind, this publication suffers from inbuilt problems. Freud’s works are, for a start, still under copyright and control over the reproduction of them rests with the artist’s estate, which encourages the anodyne rather than the critical. Moreover, David Dawson, Freud’s assistant from 1992 and now director of the Lucian Freud Archive, is listed as one of the authors. His contribution remains opaque, but from the chapter on the 1990s onwards there is an increasing recourse to his recollections. They are not, whatever he and Gayford may think, profound. Take his remarks about Sunny Morning–Eight Legs, in which Dawson lies with a dog on a bed and a pair of legs emerges from under the mattress. ‘As the picture progressed’, Dawson is reported as explaining, ‘we [‘we’?] wanted something on the floor at the bottom … So I said, “What if I jumped under the bed?”’ Gayford’s gloss on this gnomic account suggests desperation: ‘Perhaps the fact that eight was Freud’s lucky number – occasionally bringing good fortune with bets on the horses – encouraged him to accept the idea.’ That is almost as daft as the sequence in The Agony and the Ecstasy where Charlton Heston as Michelangelo finds inspiration for the Sistine ceiling in some passing clouds.

The images in this massive work are indeed very fine, and they do reveal that Freud was, a lot of the time, a wonderful painter. But it is unfortunate that the reproduction of one of his most brilliant paintings, Two Japanese Wrestlers by a Sink (1983–7), an astonishing depiction of two running taps in a kitchen sink, is over-enlarged, so that this most crisp of studies is blurred and loses its impact. There is a moral in that.