JOHN STUART MILL would be shaking his bald head with a combination of dismay and bewilderment. The author of On Liberty, who was born 200 years ago today, would be as appalled by the current assault on civil liberties as by the shocking failure of its critics to find a vocabulary with which to rally mass opposition. Now, more than ever, we need to reacquaint ourselves with the wisdom of the last great English polymath.

Mill’s upbringing at the hands of a bullying parent gave him an early distaste for tyranny. His father set out with the explicit aim of creating a genius, shielding his son from other children of his own age. He was forced to learn Greek from the age of 3, and by 8 had read Aesop’s Fables, Xenophon’s Anabasis and was acquainted with Plato’s dialogues. “Of children’s books, as of playthings, I had next to nothing,” he wrote in his heartrending autobiography. It is, perhaps, unsurprising that he devoted his life to an assault on authoritarianism.

But what is both surprising and disturbing is that his pioneering ideas are being distorted by both sides of the current debate on civil liberties. Aided and abetted by the hysterical rhetoric of the Left, successive Home Secretaries have successfully portrayed critics as ivory tower intellectuals more concerned with abstract principle than the threat posed by Islamic fundamentalism. Indeed, The Sun — that dependable barometer of public opinion — is pressing the Government to go even further.

Mill would have had none of it. Unlike modern freedom fighters, Mill was a hard-nosed pragmatist who recognised that public policy is (and should be) judged by its consequences. He would not have wasted his time banging on about Magna Carta at the very moment that citizens are worried about getting blown to smithereens on their way to work.

Mill’s great achievement was to anchor his defence of liberty not in the vague concept of human rights but in the terra firma of general welfare. He would have accepted Tony Blair’s contention that, in extreme circumstances, civil liberties must be compromised in order to bolster security, but would have ridiculed the assertion that this will be the net effect of the recent (and looming) batch of illiberal statutes. The Government’s error has not been to exaggerate the threat of terrorism but to underestimate the destructive consequences of diluting hard-won freedoms.

This was Mill’s sternest warning and it echoes down the centuries to anyone willing to sit up and listen. He understood that human advancement is conditional upon individuals having a sphere of personal freedom unencumbered by third parties, including the State. This principle has been compromised by the incitement to religious hatred provision and the glorification clause in the anti-terror Bill, and will be deeply violated if ID cards are ever allowed to become law.

Writing at the peak of Victorian conformism, Mill was confronted by the dead hand of cultural and intellectual homogeny and was appalled by it. He saw the dark places to which it could lead. That is why he defended the individual’s right to err (and, for that matter, to ridicule, offend and insult) not with the sanctimonious language of the left-wing press during the trials of Nick Griffin and David Irving but as an empirical imperative.

He wrote: “The amount of eccentricity in a society has generally been proportional to the amount of genius, mental vigour, and courage which it contained.” And later: “He who knows only his own side of the case knows little of that.” Sir Karl Popper took this analysis to its breathtaking conclusion when he demonstrated that dissent is not merely a contingent but a necessary condition of political and scientific progress.

The impressive scope of Mill’s radicalism is measured by him not only providing history’s most robust defence of liberty but also risking ridicule by extending his analysis to the treatment of women. The Subjection of Women remains one of the great early works of liberal feminism. He also developed trade theory in a way that demonstrates to any mathematically literate person why the anti-globalisation protesters are off their heads.

But there is more that Mill has to say on matters of contemporary significance. He grasped the truth that morality has meaning only when applied to entities that are conscious. From the absurdity of the Human Tissue Act (which puts the interests of corpses above those of patients waiting for an organ donation) to global timidity on pioneering genetics, Mill would have crusaded against those who put sectarian principle before aggregate utility.

Even Mill’s own life is a morality play with contemporary resonance. After his austere upbringing, he suffered a nervous breakdown in his early twenties. He found salvation in the poetry of Wordsworth. “And, when the stream/ Which overflowed the soul was passed away,/ A consciousness remained that it had left,/ Deposited upon the silent shore/ Of memory, images and precious thoughts,/ That shall not die, and cannot be destroyed.”

Few thoughts are more precious than those conceived by a humane and often troubled Englishman born two centuries ago.

Times Recommends

• Five golden rules for regulating banks
• Uighurs’ cry echoes round the world
• It is not just democracy that is illegal