Among the documents in the West Sussex Record Office is an indictment for sedition of a certain William Blake. During an altercation in a Felpham garden in August 1803, he is accused by one John Scofield, a soldier in the British army then at war with France, of having shouted: ‘Damn the King. The soldiers are all slaves.’

Fortunately for the accused, when the case came to trial in Chichester the following January the ‘invented character’ of Scofield’s evidence was judged to be ‘so obvious that an acquittal resulted’. It looks as if Blake got off lightly. Had the judge been better versed in the work of our great artist-poet, he might have noticed that Schofield’s accusation had the ring of truth: this was exactly the sort of curse that Blake – obsessed with enslavement, mental and physical – would have uttered. His prophetic books are full of contrasts between images of liberation and figures in chains – including a naked, manacled ‘Skofield’ dragging his leg irons towards the gate of Hell in Jerusalem: The Emanation of the Giant Albion (1794–1820).

In his ‘Illuminated Prophecies’ Blake pioneered a crossover between superhero comics and political zines

Like many of his countrymen, Blake had supported the French revolutionaries before the Terror. Along with other radical nonconformists he saw the turmoil unleashed by revolutions in America, France and Haiti as a fulfilment of the prophecies of Revelation, destined to sweep away the old corrupt order and ‘drain the swamp’. Instead of an isolated crackpot crying in the wilderness, the Fitzwilliam’s exhibition seeks to reposition him as a member of a millenarian generation of artists searching for spiritual renewal through art. The trouble is that the works of George Romney, John Flaxman, Henry Fuseli, Philipp Otto Runge and Caspar David Friedrich mustered in support of this view succeed only in making Blake seem more unique.

For a start, there’s his means of expression. Romney shared, even exceeded, Blake’s revolutionary fervour – he visited Paris after the Revolution – and planned an influential painting of social reformer John Howard visiting prisons and plague houses, for which the dramatic drawings on display were preparations. But Blake campaigned through words as well as pictures. Thanks to the ‘illuminated printing’ technique reportedly revealed to him by the spirit of his dead brother Robert, he could combine text and images on the same page with ease. He didn’t need to be fluent in mirror writing like Gillray. Written in varnish on paper pressed onto the plate, his God-given inspiration flowed unimpeded. Never mind the market, or the lack of one, Blake could self-publish and be damned.

The first superhero comics: ‘Laocoön’, c.1826-7, by William Blake. © The Fitzwilliam Museum, Cambridge

In his ‘Illuminated Prophecies’ he pioneered a crossover between superhero comics and political zines. All those figures with cod-biblical names locked in an endless struggle between good and evil – or, in Blake’s book, imagination and reason – are clear ancestors of Marvel superheroes and villains. But what do they stand for? Even the author doesn’t always seem sure: Urizen doubles as Jehovah and George III, Orc as revolution and Jesus Christ. Blake’s prophetic books mystified his contemporaries – ‘the conceits of a drunken fellow or madman’ was a typical verdict – and therein lies their singular appeal. His universe means whatever you want it to, its message driven home with a ‘bounding line’ that packs the punch of a propaganda poster. But as the beautiful sequence of illustrations to Milton’s Paradise Regained (1816-18) at the Fitzwilliam testifies, he could also be the most delicate watercolourist.

The show draws a parallel between the triumphant nude figure in Jacques-Louis Pérée’s ‘Droits de L’Homme’ (1795) and Blake’s resurgent ‘Albion Rose’ (1794-96); but while Pérée’s revolutionary image is just propaganda, Blake’s is art. The link with the German romantic Runge – claimed as ‘one of art history’s great missed connections’ – feels even more tenuous. Runge shared a belief in spiritual regeneration through art, but his respect for Newton’s colour theory would have made Blake see red. Neither was aware of the other’s work, and stylistically they seem to have little in common. Compared with the rank of statuesque angels inspired by a frieze at Persepolis in ‘When the Morning Stars Sang Together’ from Blake’s Illustrations of the Book of Job (c.1825), the sweet little cherubs in ‘Night’ from Runge’s engraved series Times of Day (1802-10) look like Heath Robinson water babies choreographed by Busby Berkeley.

On the plus side, the inclusion of Runge’s series is a good excuse for also featuring Friedrich’s Ages of Man cycle (c.1826) which it may have influenced, both on loan from the Hamburger Kunsthalle, a partner in this exhibition. Along with Romney’s two extraordinary ink-and-wash sketches, Friedrich’s seven exquisite sepia drawings are among the highlights of this rather muddled but absorbing show.

But I suppose it’s unreasonable to expect logic from a show about Blake. The reviewer in the Lady’s Monthly Museum had it right in 1812 when she sensibly concluded that his work is ‘too sublime for our comprehension’.