Christopher Priest is the greatest writer of literary science fiction of the last 50 years, but he now seems stuck in one of the strange illusions of time and reality he loves so much in his novels.

He moves forward and yet keeps returning to the same places and themes: magic, war, the fictional archipelago he created 30 years ago and, in his new novel, what appears to be a discomfiting fear of the foreign. This latter theme – seen most prominently in Fugue For A Darkening Island in 1972 – has re-emerged in The Adjacent. In Fugue, the subject was African immigration into Britain; in The Adjacent, the subject is Islam and a future in which the UK is a Muslim state. In Priest's version of the UK, the symbol of the army is no longer a crown and sword but a scimitar crossed with a rifle and underneath it, the shahada.

The fact that Priest is prepared to set his novel in such a world is unsettling. By writing a novel set in a Muslim Britain, he appears to be suggesting not only that it could happen but also that it must be avoided (his Muslim UK is a dystopian country that is no longer free or safe). The result – intentional or not – is the science fiction novel as a political statement. The problem with this is that the idea of the Muslim state is not well executed. It is merely the setting; a backdrop that hangs behind what's happening front-of-stage, which is another of Priest's extraordinary reality-adjusting narratives. There is no exploration of what living in an Islamic Britain would really mean.

The central character in the novel is Tibor Tarent, a man who, thanks to a space-and-time anomaly that has been adapted to become a nuclear-style weapon, exists in many different places and times. He doesn't know it, but the weapon has created versions of himself in the future and the past. It is a succession of lives adjacent to each other but invisible to each other too.

Priest delivers the idea of the adjacency weapon with great elegance and clarity. Particularly vivid are his descriptions of what it can do.

It is reassuring that Priest still has the power to summon up these strong images without the need for swirls or swoops in his sentences. There are pages from Priest's books that, years after I first read them, are still stuck, like wallpaper, to the inside of my brain. The Adjacent, despite the political flaw at its heart, has added more of them.