In the 1860s when the Austrian ambassador complained to the home secretary, Sir George Grey, about Karl Marx and other revolutionaries, he received a brief and dismissive reply: “Under our laws, mere discussion of regicide, so long as it does not concern the Queen of England and so long as there is no definite plan, does not constitute sufficient grounds for the arrest of the conspirators.”

Not quite what the current home secretary would have replied, I suspect. Theresa May is rushing yet another terrorism bill through parliament. This will place a legal duty on universities to ban radical speakers – “mere discussion” in the words of her Liberal predecessor, who probably also took a more favourable view of being labelled “radical”.

Fifty years ago Malcolm X came to speak in Oxford, an episode now recalled to stir the sentimental memories of the university’s alumni. Today, of course, he would never have made it to Oxford; the UK Border Agency would have turned him back at Heathrow. After all even the very silly, but vile, Julien Blanc, the seducers’ guru, has been banned.

Malcolm X would probably have fared better in his homeland. The United States remains a nation of laws girded by a constitution, despite police shootings and protest riots. Sadly the United Kingdom is rapidly becoming a nation of ministerial discretion and direction, ever wider administrative powers that would probably have more than satisfied the 19th-century Prussian and Austrian bureaucrats who were so worried about Marx.

Under May’s new legislation, universities will have to follow the “guidance” issued by the Home Office. If they fail to follow it, the home secretary will be able to issue them with “directions”. Far from being regarded as institutions in which the most vigorous (and contested) debates should be encouraged, higher education institutions are now to be treated as fertile ground for the “radicalisation” of gullible students by supporters of “extremism”.

This is not the first time the government has introduced legislation to require universities to ban “extremist” speakers, although paradoxically the first political intervention back in the 1980s was to stop universities, and student unions, banning rightwing speakers, extremists of another ilk.

But this initial, and rather one-sided, libertarianism was quickly succeeded by more authoritarian interventions. Until now, the centrepiece has been the “Prevent” strategy, begun under Labour and revamped by the current government.

The 2011 white paper asserted the government’s “absolute commitment to defending freedom of speech”. But, in the very next sentence, it argued that preventing terrorism meant that “extremist (but non-violent) views” had to be “challenged” – by the administrative measures it then outlined. We have travelled a long road from Grey’s reply to the ambassador.

There is so much wrong with the new legislation. The key terms such as radicalisation, extremism and terrorism will be defined by politicians who are advised by securitocrats, cowed by tabloid-inflamed public opinion and influenced by electoral advantage.

These definitions will not only, and inevitably, be politicised but are also likely to be expandable and open-ended. Those who express their opposition to UK interventions in Iraq, Afghanistan and now Syria, possibly in ill-judged rhetorical language, could well be caught in the net.

Mission drift is also inevitable. Previous anti-terrorist legislation has been used to spy on parents who might be mis-reporting their home addresses to get their children into popular schools. Botched, but costly, spying on environmental protesters has also been justified under legislation that clearly had entirely different intentions.

But the major objection is two-fold. First, academic freedom, like freedom of speech, is not something to be name-checked and then undermined. It is a fundamental principle, not because ivory-tower dons deserve to be indulged but because free universities are an essential component of a free society. The free expression of even the most detestable views should only be curbed by the most precise necessity – back to Grey’s Whiggish formula.

In the case of universities, there is an extra argument. If the war on terror has demonstrated anything, it has shown how little we in the west understand the feelings of others, or know about the countries we have invaded/liberated. To risk curbing that understanding and knowledge by discouraging the engagement and dialogue required by scholars and researchers seems perverse.

Second, banning “extremist” speakers is a counsel of despair. It accepts that such views are so seductive that they can only be suppressed. There is no confidence that, in the battle of ideas, values of openness, tolerance and liberty – those much lauded “British” values – will triumph, so we must be closed, intolerant and authoritarian (rather like the extremists we seek to oppose?).

Sadly higher education leaders, with their default pro-establishment setting, will not make these arguments – or only behind closed doors. May and her successors are unlikely to have to issue any “directions” to universities because her “guidance” will be so closely followed. In England, even amid this “clash of civilisations”, discreet pragmatism will always take precedence over open and principled debate.

Peter Scott is professor of higher education studies, Institute of Education