Protestantism was the first great Eurosceptic thing, the setting up of local power bases against a shared wisdom. Almost five centuries have passed since Martin Luther nailed (or glued? – there seems to be some doubt about the matter) his Ninety-Five Theses to the castle door in Wittenberg in 1517. Luther himself never mentioned the event.

In the year before the anniversary of that momentous act by a firebrand Augustinian friar at the age of 33, two of our finest historians have given us food for thought. Diarmaid MacCulloch, whose Reformation: Europe’s House Divided (2003) has achieved classic status, gives us a powerful set of essays, chiefly concerned with the effects of the Reformation in England. He revisits some of the main figures of the period – Cranmer, Byrd, Hooker (an especially good profile) – and gives insightful readings of the changing historiography of the Reformation phenomenon. Lyndal Roper, Regius Professor of History at Oxford, has retold the life of Luther. Hers is the bigger book. MacCulloch has wise things to say about the Book of Common Prayer, the King James Bible and the religion of the Tudor monarchs. But no one on the English scene can quite match the figure of that crazed Wittenberg friar. Indeed, there would not have been an English Reformation at all, had it not already begun in Germany.

Nor would Luther have been so famous, had not Johann Gutenberg (circa 1398-1468) invented printing, and had Luther’s inflammatory tracts – and even more so the anti-Catholic woodcuts to accompany them – not spread like wildfire, the Latin writings among the whole European intelligentsia, the illustrated ones in German among a semi-literate peasantry. At Wartburg Castle today, guides will show you the splodge on the wall where Luther supposedly threw an inkpot at the Devil. Lyndal Roper says this is a misinterpretation of Luther’s claim that he would fight Satan with ink (meaning “with printer’s ink”).

The single feeling I took away from these two inspirational books is that the Reformation was a series of political events, driven by secular concerns, in Germany by the power games of the nobility – above all of Friedrich III, “the Wise”, Elector of Saxony – and in England by the sordid politicking of Henry VIII. Until the Reformation happened, it had been perfectly possible to excoriate abuse in the Church (as when Chaucer mocked the Pardoner) without invoking Article 50.

This tolerance changed when the Holy Roman emperor Charles V convened the Diet of Worms. The assembly was intended to reassert twin bulwarks: the emperor’s personal power over huge tracts of Europe and, more specifically, the maintenance of the Catholic faith against the rumblings of the new teaching. Luther was summoned to appear before it in order either to reaffirm his views or to recant.

There was a crowd of over 2,000 people waiting to see him when he arrived in Worms, in the Rhineland, on 16 April 1521, paraded in an open wagon. The choice of vehicle was deliberate; Luther, and his followers, wanted him to be seen. This austere, still tonsured friar, with his huge, bony face divided by a long, asymmetrical nose, with dark, electrifying eyes and curling, ­satirical lips, was a figure who had become a celebrity, almost in the modern sense.

In the Germany of the 1520s, so superbly evoked in Roper’s book, people knew something “seismic” was happening. Worms is the place where Luther did, or did not, say: “Here I stand. I can do no other.” MacCulloch tells us that these are words that Luther probably never spoke, “but he ought to have said them, because they sum up a little of what it is like being a Protestant”.

Roper’s account of the diet and of ­Luther’s appearance before it is one of the most remarkable passages in her magnificent book. On the late afternoon of 17 April, he found himself standing before John Eck, the imperial orator. The papal nuncio Jerome Alexander had warned against giving Luther such publicity. Even as the titles of his many books were read out, they demonstrated, in Roper’s words, “the depth and range of Luther’s attack on the papacy and the established Church”. In reply to Eck’s questions, Luther spoke quietly, saying he was more used to the cells of monks than to courts. It was his fanbase that reported, or invented, the celebrated words.

Luther, standing alone before that assembly, is a type of what makes Protestantism so alluring. We do not need intermediaries, whether popes or priests or emperors, on our journey towards Truth; our inward conscience is king. Luther can be seen as the archetypical dissident, the instigator of what eventually became Democracy and Romanticism. But Roper’s Luther is deeply rooted in the 16th century, and in his own appalling ego. (When he was a monk, he would spend six hours making his confession.)

A large part of her story is the sheer coarseness of his language, the deranged coprology that fed his many hatreds, in particular of the Jews and of the popes. The “Devil has . . . emptied his stomach again and again, that is a true relic, which the Jews and those who want to be a Jew, kiss, eat and drink and worship . . .” he wrote. “He stuffs and squirts them so full that it overflows and swims out of every place, pure Devil’s filth, yes it tastes so good to their hearts, and they guzzle it like sows.”

The pope, likewise, was castigated by Luther as a sodomite and a transvestite – “the holy virgin, Madame Pope, St Paula III”. In his virulent text “Against the Roman Papacy, an Institution of the Devil” (1545), Luther had him say, “Come here, Satan! And if you had more worlds than this, I would accept them all, and not only worship you, but also lick your behind.” He ended his diatribe: “All of this is sealed with the Devil’s own

dirt, and written with the ass-pope’s farts.”

When you think of a world without proper plumbing, the wonder is that all of our forebears were not faecally obsessed. Luther, however, was a special case. His cloacal and theological preoccupations were inextricably linked. One of the many enemies he made in life – and most of his academic colleagues and religious allies at Wittenberg finally fell into this category – was Simon Lemnius, a pupil of Luther’s sometime ally Philippus Melanchthon. Luther said he would no longer preach in Wittenberg until Lemnius was executed, and in time he was. But not before Lemnius had written a poem that went:

You suffer yourself from dysentery and you scream when you shit, and that which you wished on others you now suffer yourself. You called others shitters, now you have become a shitter and are richly blessed with shit. Earlier anger opened your crooked mouth, now your arse opens the load of your stomach. Your anger didn’t just come out of your mouth – now it flows from your backside.

It was indelicate but true. After he escaped from Worms in disguise, Luther sometimes went for up to six days without passing a motion. The “Lord strikes me in my posterior with serious pain”, he wrote. “Now I sit in pain like a woman in childbirth, ripped up, bloody and I will have little rest tonight.” And with the constipation came visitations from the Devil. “I have many evil and astute demons with me,” he wrote at this time, surely accurately.

The man’s very name has lavatorial connotations. As he told his table companions in 1532, his “Reformation moment”, his central theological idea – that the just shall live by faith alone – came upon him “like a thunderbolt”, in the privy tower of the monastery at Wittenberg. Thereafter, Luder, which was his father’s surname, became known as “the Freed One” (in Greek “Eleutherios”, in modern German “Luther”). Conversion was a laxative.

Roper argues that “we probably know more about his inner life than about any other 16th-century individual”. As a husband (which he became when he abandoned his Augustinian vows and married Katharina von Bora, a Cistercian nun 15 years his junior), he could be genial and loving. His household was clearly a place of hospitality. And yet, even by the standards of the age, he was harsh. When his nephew Florian took a knife from one of Luther’s sons, he wrote to the boys’ schoolmaster asking him to beat Florian every day for three days until the blood ran: “If the [arse-]licker were still here, I’d teach him to lie and steal!”

On the larger, national scale his political activity makes for painful reading. Without the patronage of Friedrich III he would never have got anywhere. The agricultural workers who heeded his rallying cries did so because of the absenteeism of the Saxon bishops and priests. Yet when the Peasants’ War broke out, inspired mainly by Luther, he accused them of doing the Devil’s work. After thousands had been put to the sword, his comment was that “one must kill a mad dog”. The Magdeburg preachers rightly called him a “flatterer of princes”.

And yet, as Roper leads us through the unfolding of the Reformation by way of the psychological experiences of this monster/master thinker, there is something thrilling going on here. No one has ever equalled Luther in the extent to which he teased out the radicalism of Christianity: Paul’s theology filtered through Augustine, but honed to its existential extreme in the German preacher. “I do not wish to be given free will!” he exclaimed. He anticipated the determinisms of Darwin, Marx and Freud.

His starting point was the sheer irrelevance of either human will or human reason in the grand scheme of things. Other Reformation figures took as their starting point the ineluctable sinfulness of all human action, the impossibility of our earning salvation or working for grace. None expressed himself with quite Luther’s vigour and, yes, poetic force.

Roper reminds us that his translation of the New Testament from the Greek, which was accomplished at top speed, was “a work of genius. Luther’s New Testament reshaped the German language itself . . .” And it is no surprise, she notes, that the Faust legend began to locate the scholar-egomaniac’s journey in Wittenberg. No surprise, either, that Hamlet studied there. This is the place, for good or ill, where the individual consciousness stood up against the group. No sooner had it done so than private judgement, paradoxically, began to debunk the freedom of the will. Luther’s

response to a hundred years of humanist wisdom and the revival of Greek learning was to distrust the “damned whore, Reason”. In this, and in his pathological anti-Semitism, he was sowing teeth that would spring up in later centuries as dragons.

Many would regard the end of monastic life as the greatest tragedy of the Reformation. Civilisations need men and women who retreat from the conventional burdens of property and carnality to find something else, whether they are Pythagoreans eschewing beans or Buddhist monks wandering the Indian countryside with begging bowls. The ruined British monasteries remind us of what was lost from our philistine land (not least, women’s education). Diarmaid MacCulloch, in a fine essay on Henry VIII, says that “at no time” during the eight years when most of the religious houses in Britain were destroyed “did the government officially condemn the practice of the monastic life”. Surely that makes it more, not less, painful. They were eliminated merely for money. At least Luther, in his angry way, did object to the monastic life on principle. He came to oppose the thing that most of us would think religious houses were for, namely their quietness. One of the most fascinating things in Roper’s biography is the discussion of the concept of Gelassenheit, or calm, letting go.

MacCulloch finds this beautiful quality in the Church of England, and concludes an essay on “The Making of the English Prayer Book” with a sense of the “gentle . . . understated hospitality” of Anglican worship, and its feeling, conveyed in George Herbert’s “Love bade me welcome” of . . . well, of Gelassenheit.

No modern pope would dispute Luther’s view that it was wrong to sell indulgences. Most of the abuses of the Catholic Church to which he objected were swept away by the Church itself. Both of these books will divide us. Some readers will finish them with a sense that the Reformation was a spiritual laxative by which constipated Luder became the liberated Eleutherios, thereby loosening and releasing the Inner Farage of northern Europe. Other readers will be ­sorry that the Catholic humanists such as Erasmus and More did not win the day. For such readers as this, Luther and pals must seem like brutal wreckers of a cultural cohesion that we still miss.

A N Wilson is most recently the author of “The Book of the People: How to Read the Bible” (Atlantic Books)

Martin Luther: Renegade and Prophet by Lyndal Roper is published by The Bodley Head (577pp, £30)

All Things Made New: Writings on the Reformation by Diarmaid MacCulloch is published by Allen Lane (450pp, £25)