The fashion that he created for depicting the human form swept through court. Vanity had been frowned on by earlier Catholic generations; painting had traditionally been religious in subject and iconic in form. But Martin Luther (and others beginning to be known as Protestants) were teaching respect for the individual and his private relationship with God. Paintings that showed God’s workings in a human face chimed with these new ideas.

The result, as visitors to the Holbein exhibition at Tate Britain will see, is history brought magnificently to life. The years from 1526 to 1543, when Holbein died, saw England transformed as Henry VIII broke with Rome, married and remarried. Through Holbein’s work we know what the leading characters of those turbulent years looked like. From the slab-faced, narrow-eyed Henry to the brooding Sir Thomas More and the calculating mastermind of English Protestantism, Thomas Cromwell, the faces are as alive now as they were almost 500 years ago. They are the images that have defined that period of our history for every subsequent generation.

Holbein’s relationships with the protagonists in this struggle began before he came to England. Derek Wilson’s wonderful biography, Hans Holbein: Portrait of an Unknown Man, updated and republished this month, describes in spare, vigorous prose how the painter struck up friendships with progressive thinkers while still a young man working in Basel. Far from being crushed by the Reformation, when Switzerland’s churches were desecrated, then whitewashed — a tricky turn of events for a painter — Wilson argues perceptively that Holbein was energised by the new thinking.

He certainly made friends with the waspish humanist Desiderius Erasmus — the nearest thing the 16th century had to a contemporary celebrity. Erasmus got a commission for Holbein from his dearest friend in London, Thomas More, and it was More’s support that set the artist’s English career in motion.

Holbein is best known for his later work, powerfully projecting the image of the Tudor regime — in the shape of a massive, gilt-encrusted, cod-pieced king, representing stability and authority, and his family. Holbein’s patron by then was Thomas Cromwell, who was running a propaganda campaign to convince Roman Catholics that Henry VIII could combine being monarch and head of the national Church of England. Holbein’s Tudor pictures weren’t just expressions of his own enthusiasm for England’s relatively bloodless religious reform. They were visual propaganda for Cromwell.

Yet Holbein’s artist’s complexity is best shown by an earlier picture — which, sadly, was too delicate to be moved from the National Gallery for the exhibition.

The Ambassadors is an enigmatic work. It was painted while More, a one-time humanist who became a harsh defender of the Catholic tradition, was beginning his suicidal act of opposition to Henry’s break with Rome (which ended with his execution).

The picture shows two French noblemen standing beside an assemblage of globes, astronomical and musical instruments and books, with a half-hidden crucifix at one side, and a distorted, sideways skull superimposed in front.

It is full of hidden messages that enthralled me for a year while I was writing a novel about Holbein at this turning-point in his life.

Wilson’s analysis (which echoes the odd, raw but ingenious work of another Holbein enthusiast, Jack Leslau) shows this portrait, and one of Holbein’s portraits of the More family, to be laments for the passing of civilised humanist inquiry and free thought in a new age of violent religious bigotry.

A brief review cannot do justice to Wilson’s complex tour de force of visual detective work. But it centres on a painterly pun. Two strong diagonals — the memento mori skull pointing sideways and upwards to the centre right of The Ambassadors, and a line of hands and daggers pointing downwards to the centre right — draw the eye to the purplish-brown robe of one ambassador. This was a popular colour at the time, known as mulberry — and the Latin name for mulberry was morus. Thomas More’s Latinised name was also Morus, and he enjoyed the pun enough to grow mulberry trees in his garden at Chelsea, where Holbein lived when he first came to London.

Wilson reads the painting as a mark of affectionate regret for More’s downfall — a coded gesture of respect for a man who, even if he had become a Catholic hardliner, still symbolised, to his painter protégé, the Renaissance learning of the previous generation.

The doubt that this implies about the rightness of the Tudor regime that did for More is, of course, at odds with the enthusiasm that Holbein was later to show for Henry VIII. Yet Holbein’s ability to feel these half-concealed, bittersweet nuances of regret and admiration — and to convey them so subtly in one of the world’s most thought-provoking paintings — make of him both a greater artist and a bigger man.

Portrait of an Unknown Woman, by Vanora Bennett, is published next month by HarperCollins, £15. Offer £13.50

Times Recommends

• Sarah Palin and the Palindromes: 7 extraordinary connections
• Physics for Future Presidents: The Podcasts
• 10 Books Not To Read Before You Die