In these days of alternative facts, perhaps alternative-world stories can lead us closer to the truth than conventional social novels. These two books are great examples of what the critic John Clute calls “fantastika”. Both are wholly idiosyncratic and very impressive. They are about as serious as you can get while remaining absorbing as fiction. The poet, sculptor and painter Brian Catling is professor of fine art at the Ruskin School in Oxford, while China Miéville is a fantasy fiction writer as well as a former parliamentary candidate who has published Marxist essays and is a co-founder of Left Unity. Both books show a sophisticated enthusiasm for the surrealists and their predecessors, and both are fascinated by magic and shamanism. And thankfully, neither novel has a juvenile or pseudo-juvenile protagonist, nor is there an elf or dragon in sight.

Brian Catling’s The Erstwhile, like the work of Mervyn Peake, is outside genre. The stand-alone centre novel in a three-decker, it is even better than The Vorrh, the volume that preceded it. If the book has a significant influence, it is Raymond Roussel’s Impressions of Africa, which has inspired surrealists, absurdists and symbolists, including Breton, Cocteau, Dalí, Boris Vian, Robbe-Grillet, Borges, John Ashbery, Foucault and others, since 1910, and it is from Roussel that Catling takes the endless forest known as the Vorrh. At its centre he locates the Tree of Knowledge, once guarded by angels who betrayed God’s trust, let Adam eat its fruit and degenerated to become inhuman brutes.

Most of these fallen angels – the “Erstwhile” – have buried themselves in the forest. A few are scattered about the world, some are deep in the earth and some have become almost human, especially in London. It is here that one Bedlamite was discovered in the Thames mud at least two centuries earlier and was cared for by William Blake, who drew his portrait as Nebuchadnezzar and whom he calls “my old man”.

Various interests outside the Vorrh need to find the Erstwhile. European logging companies, anxious to have them back to use as slaves, hire a bunch of heavily armed brutes and weirdos to take a steam locomotive into the forest, beginning a singularly ill-fated chain of events yet making a hero of Ishmael, the nearest thing to a protagonist. Others with mysterious, barely articulated motives come and go, hatching intricate plots, wreaking ancient vengeance, recalling forgotten lives and places.

Again we meet a variety of wonderful, often bizarre, characters: a woman impregnated by robots, a troubled young Cyclops corrupted by life in the decaying European colonial city on the edge of the Vorrh, an ancient family of half-human Bakelite robots, Blake and, in Bedlam, Louis Wain, the mad cat painter. The plot is complex, monumental, engrossing and crammed with original images. If you like Peake’s Titus Groan, Cat­ling’s splendid novel is probably for you.

While The Erstwhile is inspired by surrealism, Miéville’s novella is about surrealism and how transgressive art and visionary science can be perverted to serve reactionary purposes. In 1941, after the capitulation of France, people crowd the ports attempting to escape the Nazis. A bunch of surrealists major and minor and their hangers-on, petitioning for visas in Marseilles, invite a young American rocket scientist back to Breton’s villa. He is a Crowleyite magician desperately trying to get to England with a device that he is sure will defeat the Nazis. While the surrealists play fanciful games with absurd ideas and images, he uses his mysterious machine to record their inventions, which he finds irritatingly whimsical. The device is stolen and sets off the “S-blast”, an explosion of surrealist energy.

Leap forward to 1950: an endless war is being fought in Paris between the Germans and their demonic allies and various rival ­resistance groups. Thibaut, who has an encyclopaedic knowledge of the surrealists and their influences, is a fighter with the Main à plume, a group that uses living surrealist images to attack the invaders. The city is controlled by arrondissement and some sections are safer than others: you can lean on a lamp-post looking into sunlight in one direction and into night in another. Weapons can manifest all kinds of monstrosities and lethal whimsicalities. The Nazis retaliate with horrible creatures converted to their service or created by perverse science. And, as Thibaut discovers from a dying Englishwoman who rides Leonora Carrington’s “Amateur of Velocipedes” (half bicycle, half woman) against the Nazis, they are preparing “Fall Rot”. But what is Fall Rot? And what do the Nazi Catholic priest Robert Alesch and the Auschwitz physician Josef Mengele have in common?

The best of Thibaut’s group are ambushed and killed. With his gift for distinguishing between authentic surrealism and faux-art, and thus telling which creations are allies and which are Nazi, Thibaut fights on, joining forces with the manifestation of Breton’s Exquisite Corpse and Sam, a photojournalist who claims to be recording events for her book The Last Days of New Paris. Her camera has interesting properties. Thibaut doesn’t entirely trust her but accepts her as an ally while they continue to investigate the mystery of Fall Rot. They discover that the plans Mengele and Hitler have made for Paris are the essence of profound evil, as attractive and persuasive as only evil can be. Miéville’s subtle understanding of politics, married to his sophisticated interest in science and art, gives us a short tale that is packed with ideas and inventions.

Can there be such a thing as genuine Nazi art? Is transgressive art naturally allied with the left, and is it therefore a natural enemy of the right? What is “decadent” art? Miéville puts all these questions and arguments in the context of a page-turner whose end left me almost physically applauding.

Miéville identifies with the “New Weird” movement, a development of what used to be known as “science fantasy” – a blend of the occult and scientific speculation that was the province of C L Moore and Leigh Brackett, appearing in the most garish pulp magazines (which were my favourites): Thrilling Wonder Stories, Startling Stories, Planet Stories. The New Weird produces mostly urban fantasy with a moral point and, at its best, it combines the virtues of visionary fiction and horror fiction, political satire, literary fiction and even historical fiction. But is it art? That’s a question that Miéville asks and Catling answers.

Michael Moorcock’s most recent novel is “The Whispering Swarm” (Gollancz)

The Erstwhile by Brian Catling is published by Coronet (462pp, £20)

The Last Days of New Paris by China Miéville is published by Picador (224pp, £14.99​)