On the first floor of the Courtauld Gallery there is a portrait of Sir Thomas Thynne, painted in the last decade of Sir Peter Lely's life, and gazing at a room of similarly confident characters. You know the sort of thing: ancestor to the Marquess of Bath and the late Diana, Princess of Wales, heir to Longleat, and politician, shortly to be murdered in Pall Mall, he is all bundled up in scrunchy rose madder satin, and casts a noble shadow – the very essence, in short, of the aristocracy in oils. And it is worth visiting Sir Thomas on the way up to Peter Lely: A Lyrical Vision, to put into perspective the rest of this arresting exhibition. For here are not the towering landowners and puffy-jawed heiresses that hover on the walls of the stately homes of England, but peachy-buttocked nymphs, gnarled artisans and music-makers, entranced by their art.
Lely was the name chosen by Pieter van der Faes when he set out from Holland in the early 1640s for fame and fortune in the English court. Inspired by the floral decoration on his family home in The Hague, and variously spelled, the name suggested the ornamental opulence that would appeal to his extravagant patrons, above all Charles II. But before leaving his native country he began on the 30 or so narrative paintings, of which the Courtauld owns Reuben Presenting Mandrakes to Leah. In this Old Testament scene, the childless Rachel intercepts Leah's order of mandrakes, said to aid fertility, in the hope of conceiving, and trades her night with the women's shared husband, Jacob. Lely's Leah is no advertisement for motherhood, her thick neck and flattened features inclined towards imperious Rachel. Nor do the mandrake mule – eldest child Reuben – and the other gargoyles stuffed around Leah trigger broodiness. But there is something in Rachel's disdain that feels familiar: Lely was an admirer of Titian – and would not only view his work in print form and in his wealthy patrons' homes, but purchase it, too. If he had not actually seen the fury of the goddess espied naked in Titian's Diana and Actaeon, he certainly knew something of a demanding woman's capacity for rage.
Everyone is altogether more cheerful, as the intended male viewer will be, in The Finding of Moses (1641), painted in Holland and the earliest picture in the exhibition to capitalise on the potential in both Old Testament and mythology for naked female flesh. Pharaoh's daughter, companions and attendants, one still wringing her hair after bathing in the river, are so surprised by the emergence of a baby from the floating basket, that they don't notice their clothes are slipping off again. Europa and her maidens are similarly challenged as they make garlands for Jupiter, disguised as a supine white bull. Fan of Titian as Lely was, how he would surely have loved to have confected that master's Rape of Europa, now in Boston: Titian's massive animal crashes, wild-eyed, into the waves, while Europa balances precariously between defilement and death by drowning. But movement is not Lely's strong point. His Europa contains one stumpy outstretched arm to suggest action; when it comes to passion, its drowsy aftermath is safer terrain.
Nymphs by a Fountain (circa 1654) with its suggestive water spout is dominated by the anterior and posterior views of already exhausted nudes, the parted garment of one revealing a shadow of pubic hair, the other, turned away, nonchalantly signalling the point of entry with a drooping hand. This was just the sort of thing to delight Charles II, three years on the throne. Lely's place in Restoration England was secure. And lucrative: alongside this exhibition runs one of drawings from the artist's collection of thousands, including works of breathtaking accomplishment by Parmigianino, and a copy of what is thought to be an early design by Michelangelo for The Last Judgement at the Sistine Chapel, a virtuoso display of muscular complexity that Lely, his early models invested with sausage limbs, could only dream of. He knew he must improve: in his own drawings made in 1665 of hands and arms he does his anatomy homework.
The security of royal patronage squashed art for art's sake: no more urchin boys in the manner of Caravaggio, as in the Tate's Boy Playing a Jew's Harp (1648-50), his luscious, possibly purloined, sash a hint at the voluptuous fabrics of affluent sitters to come. And no more infants, as lovely as Leah's are lumpen, carefully picking their way through a part-song as in Two Children Singing (1650). Music was Lely's pastime, and is the theme of the picture that dominates the show, The Concert, painted circa 1650, and showing, it appears, Lely himself on the bass viol. Behind him, an angelic young woman looks frankly at the viewer, a little flautist and second child to her right; and, between this group and two divine figures encased in a shower of red satin, is a female singer, her blue gown falling from a naked back.
Whatever its intended meaning, The Concert amply illustrates the amateur musician's departure from home-spun amusements to the blandishments of the court, from the open air to suffocating high society and Sir Thomas Thynne. But is this exhibition the end of that journey? The curator, Caroline Campbell, believes other narrative pictures are yet to come to light under the names of other painters, in châteaux, Schlösser or British attics. If there are underdressed damsels wilting by your header tank, you know who to call.
To 13 Jan (020-7848 2733)
See a new side of Barbara Hepworth at The Hepworth Wakefield Gallery where her series The Hospital Drawings, delicately showing surgeons at work, is on till 3 Feb. The winner of the Taylor Wessing Photographic Portrait Prize was announced last week – congratulations, Jordi Ruiz Cirera. Drop into the National Portrait Gallery to see if you agree with the judges' choice (till 17 Feb).