The Police, Fire and Crime Commissioner for Northamptonshire, Danielle Stone, told a panel she and Balhatchet were not made aware of the proceedings for contempt until October last year, but acknowledged there were “huge questions” about the chief constable’s apparent lack of awareness, and has launched a review.

Against an impenetrable black ground, the crucified figure looms pale and shining. There’s almost no colour, beyond the trickle of blood on Christ’s feet from the nails driven through his flesh. His head slumps, and his carefully modelled face is at peace (no agony here). But the most striking part of the picture is surely the loincloth, which folds and crumples and bunches around his midriff – you can imagine passing your hand over it, feeling the linen’s volume and texture. In its original home, the monastery of San Pablo el Real in Seville, the painting was displayed with “little light”, according to the 17th-century Spanish artist and writer, Antonio Palomino. “Everyone who sees it, and does not know it, believes it to be a sculpture.” The paleness of the body, the fabric, must have loomed out of the dark like a vision.

Francisco de Zurbarán, who painted this solitary crucified Christ, is one of the three great artists of the Spanish 17th century. But, unlike his peers Velázquez and Murillo, he has never had a show to himself in the UK – until now, as his work forms the basis of a major exhibition about to open at the National Gallery in London. Compared with his precise contemporary and friend Velázquez (born in 1599, a year after Zurbarán), his work can seem stilled, becalmed. You can see the contrast clearly, in works commemorating Spanish military success that each of them were commissioned to paint for Philip IV of Spain’s new palace, the Palacio del Buen Retiro. Both are now in the Prado. Zurbarán’s The Defence of Cádiz Against the English has the quality of a frieze, as the Spanish generals look down serenely at the sea battle below. Velázquez’s The Surrender of Breda is all drama, encounter: a quicksilver painting that captures time as it flees.

Zurbarán’s skill is different. His is an artist of inner vision, of meditation and contemplation. Time does not flee, but stands still. He has a paradoxical quality, making you wonder what it is that you are looking at, partly because he can make the immaterial seem solid and touchable, partly because at times his works depict two planes of reality simultaneously.

Take one of the first in the National Gallery exhibition: The Apparition of Saint Peter to Saint Peter Nolasco, the latter saint being the founder of the Mercedarian order of friars, whose mission was to recover fellow Christians who had been captured by Muslims during conflicts in the Mediterranean. (The work was one of two dozen commissioned in 1629, early in Zurbarán’s career, for the monastery of the Merced Calzada, Seville, now visitable as the city’s Museum of Fine Arts.)

St Peter Nolasco is on the right, enrobed in white, and he “sees” St Peter – crucified upside down – hovering on a backdrop of ochre clouds. But St Peter Nolasco hardly seems to be in the realm of the real himself. We are not “with” him, wherever that might be (the shadowy background is entirely abstract). The painting seems to be offering itself as a double refraction of unreality, as if it was itself a vision.

There were good theological reasons for painting like this at the time: in the wake of the Council of Trent, whose deliberations defined the Counter-Reformation, religious art was charged with a direct, clear purpose: to move the viewer to devotion. Aside from the year or so that he spent in Madrid painting for the court in the mid-1630s, his career was largely based in Seville, and his clients were mostly the hugely powerful religious foundations of the city and the wider region.

Just then, Seville was wildly prosperous. Since 1503, it had had a monopoly on trade with Spain’s viceroyalties in the Americas – a status of which Zurbarán took advantage, sending out over 100 canvases for export to Lima, Buenos Aires and elsewhere. Zurbarán did provide secular scenes for Philip’s Buen Retiro – aside from his sea battles at Cádiz, 10 paintings of Hercules pounding through his labours, as well as a curious, colossal head of a man that startles when it is glimpsed through the enfilade of rooms in the National Gallery. But it is in paintings of the divine and the spiritual that he excelled.

Sometimes these commissions were on a stunning scale, and must have required a busy studio – as in the 24 paintings for the Merced Calzada in Seville, or the 15 x 10m altarpiece for the Carthusian monastery of Nuestra Señora de la Defensión, just outside Jerez de la Frontera. The last monks moved out recently, and it is now possible to visit the honeyed-stone establishment, with its baroque facade stuck on to the front of the former 15th-century Renaissance frontage. But there in the church you have to imagine the full force of Zurbarán’s altarpiece, with its dozen paintings set between gilded sculptures since, in the wake of the Napoleonic wars and the dissolution of Spain’s monasteries in 1835 these – like many other works in Spanish churches – were sold off and scattered.

Scholars have debated the altarpiece’s original layout. The National Gallery’s putative reconstruction has Zurbarán’s enthroned Virgin in the most prominent position, flanked by his Adoration of the Magi and Circumcision. If the gallery is right in supporting this reconstruction, it will be the first time the works have been set alongside each other since the dissolution.

From the vast in scale to the intimate and hushed: some of Zurbarán’s most arresting works are not these busy, exciting scenes of saints and biblical stories but his remarkable small-scale still lifes. He was an extraordinary painter of the texture and weight of things. In a work in Seville’s Museum of Fine Arts – not in the London show – the most thrilling part of the scene of St Hugh’s visit to the founders of the Carthusians is, to me, not the miracle of the meat turning to ash, or even the austere faces of the monks, but the exquisite breadiness of the bread rolls, and the smoothness of the blue-and-white ceramic carafes that, at the base, turn rough and unglazed.

Zurbarán’s son Juan – who died in the catastrophic outbreak of plague that robbed Seville of its prosperity and half its population in 1649 – made still lifes that provide an interesting contrast to his father’s. They are more luscious, more overflowing with lilies, marigolds, jasmine, pears and lemons than his father’s, where each object sits in its own space, self-contained. As in his paintings of visions of the divine, a small-scale row of dishes and vases made late in his career, around 1650, shines out against a sepulchral background.

An earlier work, from 1633, has a dish of citrons reflecting gold into their silver platter; a basket of oranges complete with a twig of leaves and blossom (accurately, since oranges flower and fruit simultaneously) and a cup of water sitting in a silver dish with a rose lying on its rim. The fruit and the flowers can be read as symbols of the divine. But as with Zurbarán’s paintings of visions, these works seem to invite you into the illusion that you are seeing tangible things, objects over whose surfaces you want to run your fingers – and something otherworldly, things prompting contemplation of the supernatural.

The ambiguity in what we are being invited to see is at its strongest and most compelling in the final work in the exhibition. It is small, and you might whisk past it as you head for the exit, mistaking it for just another crucifixion with a praying figure in the foreground. But look again: it turns out that the figure standing before Christ – against another of Zurbarán’s darkened backgrounds – is a painter. In his left hand are brushes, and a palette loaded with paints that are surely just right for making the figure’s very own flesh tones and robe. The artist’s right hand is clamped to his heart, his ruddy face looking upwards in awe at his saviour – who, by contrast, is grey of skin and quite dead.

Who is this figure with his paints standing at the foot of the cross? At times he has been identified as St Luke, patron saint of artists. But it’s irresistible not to consider him, in a sense, also Zurbarán himself. It’s impossible not to think about the very act of painting when looking at this work. Painting as an act of devotion, wonder and prayer. Painting as a means of seeing the divine. Painting as a way of imparting visions that hover between the real and the unreal, the illusory and the tangible.