In 1800, William and Catherine Blake left London and moved to the village of Felpham, in Sussex. The previous years in the capital had not been kind to them and as they left the city they were filled with optimistic hopes that a new life on the south coast of England awaited them, near to Blake's new patron, the liberal poet William Hayley. Three years later, demoralised by his labours for Hayley and regular illnesses that afflicted Catherine in their damp cottage, disaster struck when Blake was caught up in an argument with a soldier, John Scolfield, and was tried for using "seditious and treasonous expressions" against the King. No longer a place of opportunity, the Blakes returned to London much chastened.

And yet Blake's time in Sussex did mark a series of new beginnings. It was during his three years in Felpham that he composed the beginnings of his most ambitious illuminated books, Milton a Poem and Jerusalem the Emanation of the Giant Albion, in particular apparently writing the lines that would, a century after his death, become the hymn "Jerusalem". Likewise, this was an opportunity for new experiments in tempera painting and, via acquaintances with many of Hayley's friends, including George O'Brien Wyndham, 3rd Earl of Egremont, and his mistress and then wife, Elizabeth Ilive, Countess of Egremont, Blake came to produce some of his most ambitious works, most notably A Vision of the Last Judgement.

It is works such as these, as well as the influence of the Sussex coast on Blake more generally, that are the subject of an exhibition at Petworth House, the stately home of the Earl and Countess of Egremont, William Blake in Sussex: Visions of Albion. Housed in the former servant's quarters, the exhibition itself is not especially large but is extremely rich in terms of the objects collected there, bringing together a selection of Blake's paintings and prints created during his time in Felpham or, as with the Last Judgement, produced for commission shortly after his return to London. Alongside these are examples of works collected by Egremont and his wife, such as two copies of The Book of Job and an illustration of The Characters in Spencer's 'Faerie Queene', as well as works that drew on the Blakes time in a rural landscape and documents from the trial for sedition.

The exhibition, following on from similar ones for Turner and Constable, has proved to be very popular and, on the day that we visited, was sold out for the day with a steady stream of visitors to view the carefully curated and beautifully presented selection of works. It certainly works as a coherent collection and, in contrast to more typical settings alongside huge works in the "Grand Manner" that comprise the rest of the Petworth collection Blake's work is not overwhelmed in sheer scale as would happen in more open settings. It is often a surprise when seeing works close up just how small they may appear compared to the vastness of Blake's imagination: one delightful effect of this was to observe how visitors would lean into certain works, poring over the intricate details that bustle through Blake's apocalyptic scenes.

While the Last Judgement is undoubtedly the star of the show, two other images particularly struck me because they are so rarely reproduced. The first, a hand-coloured print of Little Tom the Sailor, a ballad composed by Hayley and illustrated by Blake to raise funds for a local widow, is astonishing for a variety of reasons. Hayley's poetry is, frankly, dreadful, and compares poorly to Blake's own verse on innocence, and yet the illustrations for this ballad are vivid invocations of the style that the artist will return to in his woodcuts for the edition of The Pastorals of Virgil published by Robert J. Thornton in 1821 (also on display here). Similarly, The Fall of Man, a pen and ink and watercolour composition produced for Thomas Butts in 1807 is presented next to the more famous A Vision of the Last Judgement and is breath taking in its scope. Ostensibly depicting the moment of Adam and Eve's expulsion from Eden in the final book of Paradise Lost, it not only contains a complete history of that poem within its modestly-sized canvas, but also incorporates a truly radical interpretation of the biblical event. Whereas it is the angels who enact God's will in barring Adam and Eve from the Garden of Eden in Milton's version, Blake has a humane and kindly Christ lead them forth into the world as God the creator mirrors the posture of Satan in hell at the foot of the painting. Motifs of threatening animals prefigure the style that Blake will return to in his later illustrations to The Book of Job, and a particularly compelling detail that I have never noticed before in reproductions of this painting is the head of a king that rears up miserably from a pit beneath Satan's backside. For all that he may have been cowed by the events of his trial, unlike many other Romantic artists Blake never turned his back on his revolutionary beliefs.

The accompanying catalogue, published by The National Trust and Paul Holberton Publishing with a foreword by the curator of the Petworth exhibition, Andrew Loukes, is an exceptional piece of work that brings together a number of excellent Blake scholars to contextualise Blake's work in the light of his time in Sussex. I will quickly pass over my one slight gripe at the catalogue which is that its square format, while unusual, cannot do full justice to all of Blake's images (most notably A Vision of the Last Judgement, although The Sea of Time and Space is the one image in the book that does benefit). Other than that, this is a book that deserves to be read by Blake experts and enthusiasts alike.

For the experts, with one exception this book does not especially present new scholarship. Much of the information contained here draws upon work begun by figures such as G. E. Bentley and continued in more recent years by writers such as Mark Crosby (also a contributor here) and Jonathan Roberts. For the more general reader, this is indicative that the quality of material is rooted in the grand body of Blake scholarship that has been generated in the past sixty years or so, and it is a real pleasure to me to think that a new generation of Blake admirers will have such a solid, clear introduction to the most significant aspects of post-war understanding of how the artist lived and worked.

Nor is my opening comment in the preceding paragraph regarding experts intended to be at all dismissive. The great task of a catalogue such as this is to ensure that the artist is understood and admired by as a wide an audience as possible, and William Blake in Sussex succeeds completely in this respect. However, even for Blake scholars the catalogue has an incredibly useful purpose, in that it repackages and recontextualises a considerable amount of Blake's work in the light of his experiences in Sussex. For example, I have for many years written of the importance of Blake's time at Felpham to his later prophetic works, Jerusalem the Emanation of the Giant Albion and Milton a Poem in particular: Blake's three-year sojourn beside the sea appeared to fix in his mind the form of the giant Albion in a way that had not been clear to him in London. Alongside this I was aware, of course, of the commercial engravings he undertook for his patron, William Hayley, as well as some other important commissions such as the Last Judgement for Elizabeth Ilive. I had not, however, especially considered those other commissions he continued for his longstanding patron, Thomas Butts, a second series of biblical paintings, some of which were completed at Felpham and which are examined in considerable detail in this catalogue by Naomi Billingsley. Likewise, Mark Crosby's and Martin Butlin's reflections on Blake's artistic development both as a theorist and as a watercolourist (as with his tempura "frescoes" of the poets' heads that adorned Hayley's library) was profound during his three years away from the capital. Felpham is a pause in Blake's otherwise uninterrupted obsession with London, but one that transforms his art in important ways.

The break from London also modifies his practice in a way that is somewhat obliquely alluded to by some of the writers here: Naomi Billingsley observes that his time away from the capital resulted in a greater engagement with Christianity in Blake's work, and though she does not explicitly make the link here, it is almost certainly the case that his removal from radical associates who lived and worked in London in the 1790s did somewhat soften some of his hardening attitudes to Christianity in particular, an observation that was first made by Jacob Bronowski and further developed by later commentators like David Worrall. Not that Blake could ever be fully de-radicalised: as Mark Crosby discusses at some length, Felpham is also important to Blake as the moment when he comes into clearest conflict with the crown, being arraigned at the Chichester Quarter Sessions in 1804 on charges of sedition, brought against him by Private John Scolfield. Alongside his worsening relations with Hayley, the trial - and eventual acquittal - of Blake marked a bleak ending to a sojourn that had begun with such high hopes.

Elsewhere in the catalogue, alongside reproductions of the works themselves, an essay by Hayley Flynn offers a delightful insight into how the experience of Felpham also bore fruit in Blake's later pastoral visions, most notably his woodcuts for Thornton's Virgil. For me the most original contribution (because drawing upon information of which I was not aware rather than because of the quality of its ideas) is Andrew Loukes's piece on the Petworth collection of Blake's works. As Loukes observes, the 3rd Earl of Egremont was an unusual collector, so that by "the 1820s it was possible to experience at Petworth a considerable body of works in this vein [the 'Grand Manner'] by otherwise unfashionable artists, such as the painter Benjamin Robert Haydon and the sculptor John Carew." (p. 47) It is because of Wyndham's eclectic tastes that Petworth became the only major country house to hold works by Blake and, as both the catalogue and exhibition make clear, Sussex as a county has been all the better for it.

The exhibition Wiliam Blake in Sussex: Visions of Albion continues at Petworth House until 25 March. The accompanying catalogue is now available, RRP £16.50.