Decency and Disorder, by Ben Wilson

This book explores the rise of a breed of self-righteous, evangelical meddlers who poked their nose into other people's concerns and tried to stamp out activities they saw as sinful. Yes, it is the story of the people who ended the slave trade, although Decency and Disorder: the age of cant 1789-1837 has little to say about that campaign. Instead, it dwells on the evangelicals' other interests: resuscitating old laws against swearing and sabbath-breaking, combing through libraries looking for "filth", and even trying to abolish Christmas because it encouraged drunkenness.

The connection between killjoy tendencies and the anti-slavery movement is well known, but not easy for us to understand. Our mostly secular ethic promotes personal freedom and respect for others, and deplores priggishness. From this viewpoint, the evangelical mentality seems to fall into two mismatched halves.

This book does not help us much with our incomprehension, for Ben Wilson treats his moralists with irony and often nudges us into laughter. He spends surprisingly little time on their ideological background or on their more beneficial achievements, and does not assess them on their own terms. What he does do, magnificently, is to show where we got our own aversion to much of their behaviour: how this, too, is a product of history.

His key word is "cant". It had two meanings: thieves' slang, and the hypocritical twaddling of self-appointed moral guardians. In both cases, language was used to establish membership of an in-group. That the decency cult was primarily a thing of words was pointed out by Byron: underneath the talk, he said, people behaved as they always had. (He also complained, in a letter, that life these days was "all cant and no cunt".)

The cantification of England represented a major shift of values. Britons had once been so famous for plain speaking that, in France, to "talk English" was to be offensively coarse. Even the best table-talk resounded with words like "short-arse" and "crack-fart". Yet, by the 1820s, you could not speak of a thigh of chicken in polite company, and women were "in the family way" rather than pregnant. How could such change happen in one generation?

Although the shift was quite rapid, it was neither straightforward nor uncontested. Wilson traces the underlying cause to fears of public disorder following the French revolution. Before that, mayhem was thought a price worth paying for the Englishman's sacred right to liberty. A Russian visitor in 1789 observed that the English hated being policed so much that they "would rather be robbed than watched".

By the turn of the century, the uncontrolled emotions of the poor were making people nervous. The 18th-century cult of tearful sensibility gave way to a new ideal of self-restraint, typified by Jane Austen's sternly proper heroes and heroines. Sternness could go against the grain. Britons had been generous to beggars, pressing coins randomly into outstretched hands. This was now seen as irresponsible. Giving cash only hastened drunkards and vagrants along their path to doom. The poor needed protecting from "the folly of the thoughtless benevolent", as Wilson puts it - he writes beautifully, and has a knack for spot-on phrases.

From now on the nation bristled with such organisations as the Temperance Society and the Society for the Suppression of Vice. By the 1820s, people had a sense of living in a changed world.

Public fairs had been replaced by tidy parks. Christmas celebrations continued, but would soon evolve into a Victorian family affair instead of a wild rumpus. The middle classes increasingly defined themselves in terms of decorum. Being well-off was confused with being moral, and seeming well-off was even more important; to be poor was now to be "embarrassed".

As the forces of decency marched on, they spawned a sub-culture of "fugitives from decorum", who asserted the old freedoms through bawdy plays and stories. There was also a more serious anti-cant brigade. These had their own cant, which consisted mainly of hurling the word "cant!" at the other side. The word became such a powerful weapon that it could inhibit reforms. It was used against those who wanted to ban bear-baiting and other forms of animal abuse. Even the ongoing struggle to free West Indian slaves suffered, campaigners often backing off when they heard the magic word.

Thus the two tendencies proceeded locked in step. Cant and anti-cant pushed against each other and, in doing so, propelled each other around the floor like tango dancers.

Although terms have changed, and no one now speaks of "suppressing vice", this book casts much light on our own world. Our society was created partly by the canters, but even more so by the anti-canters. The combination of widespread insincerity with vociferous accusations of insincerity has generated the miasma of distrust in which we live today. Anyone who now claims to be acting from disinterested motives in public life is taken to be canting: one reason we have lost interest and faith in politicians.

Ben Wilson is a thoroughly 21st-century writer. He never refers explicitly to present parallels, yet his book is suffused with them. His rootedness in modernity prevents him from examining hidden prejudices: he simply assumes that anything we now value (animal rights, spirited rebellion, blunt speaking) is good, and anything we don't (self-restraint, sobriety, meddling) is bad. Many would agree with him, but this is why we need historians to show us the contingency of our assumptions. Yet this fault is also Decency and Disorder's strength. It returns obsessively to material of importance to us, from how to deal with anti-social behaviour to the problems of trust and moral leadership in a cynical age. In failing to approach the past on its own terms, Wilson forces it to speak to us on ours, to riveting effect.

Sarah Bakewell's 'The English Dane' is published by Vintage