As anniversaries go, the timing could hardly be more apt. As Europe braces itself for the next Islamist attack, the next assault on our civilisation, a season of events marks the 500th birthday of a book that outlined an enlightened vision of the ideal society. Utopia 2016 is a year-long celebration of Thomas More’s Utopia at London’s Somerset House, where the Royal Society and the Royal Academy used to meet. Somerset House is a building that encapsulates the free-thinking values of the Enlightenment, and More’s Utopia is a book that encapsulates the Renaissance sensibilities that built it.

We all know what sort of society Isis wants (the clue’s in the name), but what sort of society do we want? What rights are we defending? The right to have a good time all the time? Or do we believe in something deeper? Five hundred years since it was written, under a repressive theocracy that forbade free speech and beheaded its opponents, does Utopia hold any clues?

As every British schoolboy (and schoolgirl) used to know, in 1535 Sir Thomas More — or Saint Thomas, if you’re a Catholic — got his head chopped off for refusing to recognise Henry VIII’s newfangled divorce-friendly C of E. As Henry’s Chancellor (the first layman to hold this office), More had bumped off a fair few dissidents himself, though he didn’t much like beheading them — he preferred to burn them alive (both these methods of execution seem to be similarly popular in today’s Islamic State). In 1516, the same Thomas More wrote ‘a splendid little book, as entertaining as it is instructive’ (like modern authors, he got to write his own blurb) about a fantasy island called Utopia, a prosperous republic without kings or aristocrats, where divorce is allowed, priests are free to marry, women can take holy orders and freedom of religion (even atheism) is permitted. The book became a classic (rightly so — unlike a lot of modern books that make the same boast, it really IS both entertaining and instructive), and for 500 years ever since, anyone who’s ever read it has been trying to work out what on earth he meant.

The most shocking thing about Utopia is how left-wing it seems. Even Jeremy Corbyn might find More a bit too militant. There is no money or private property on Utopia, housing is nationalised and agriculture is collectivised. There is no unemployment. Medicine and education are free at the point of use. The welfare state reigns supreme. More rails against the rich, who corner markets and create monopolies, and noblemen who live off the labour of their tenants, bleeding them white by constantly raising rents. This could be Marx talking, 350 years before Das Kapital. ‘I don’t see how you can ever have justice or prosperity so long as there’s private property and everything’s judged in terms of money,’ he says. ‘The one essential condition for a healthy society [is the] …equal distribution of goods, which I suspect is impossible under capitalism.’ Gosh.

Thankfully, there’s more to More’s Utopia than proto-socialist polemic. You don’t need to be a Marxist to think we might get a lot more done if we only worked a six hour day, or that it might be a good idea if laws were simplified, so people can understand (and practise) the law without constant recourse to lawyers. More can’t stand career politicians (any Utopian who tries to get elected is barred from public office — hurrah!) yet he doesn’t advocate outright anarchy. So long as they don’t really want the job, elected mayors are OK (good news for Boris). With its workers’ uniforms, communal dining rooms and labour camps for convicts, More’s planned economy may conjure up dark visions of the Soviet Union — but his idea of local government actually seems closer to the Swiss cantons. In Utopia modesty is a virtue, and status symbols are ridiculed. More lived in Chelsea, as anyone who’s seen A Man For All Seasons will recall. I wonder what he’d make of it today?

More’s political daydreams are fascinating (and frequently slightly barmy) but it’s his broadminded attitude to religion that makes this a textbook for our troubled times. Of course it’s richly ironic, given his penchant for persecuting Protestants, but what he wrote is what he wrote, and it’s still radical today. ‘God made different people believe different things, because He wanted to be worshipped in many different ways,’ he declares. ‘[It’s] stupid and arrogant to bully everyone else into adopting one’s own particular creed.’

Naturally, the question remains: did he really mean it? Was the whole thing a flight of fancy, a sort of Tudor sci-fi story? True, it’s presented as a traveller’s tale, told to More by a returning seafarer, yet it’s recounted with such lucid passion you feel sure he must be sincere. More may not have practised what is a sort of altruistic hedonism — a way of life that might best be described as Parisian. ‘The Utopians …regard the enjoyment of life — that is pleasure — as the natural object of all human efforts,’ he concludes. ‘We’re impelled by reason as well as instinct to enjoy ourselves in any natural way which doesn’t hurt other people.’ Five centuries on, in the long shadow of Isis, that’s still an ideal that unites us, and a creed we can all defend.