What did we learn about the British empire at school? In my case, which is the case for a generation born just before the empire’s long collapse, nothing very much. My parents and elder brother knew from their schooling about the battles of Arcot and Plassey and the lives of Robert Clive and General Gordon of Khartoum ; but though I was aware of these people and events, from family conversations and old books that lay around the house, I was never formally taught about them.

At school in Scotland, we got the Tudors and the Stuarts, Turnip Townshend and the spinning jenny, and endless weeks of the Franco-Prussian war. Though the empire lived among us in the form of tea chests, “IND. IMP.” (Indiae Imperator, or emperor of India) on coins bearing the late king’s head, and steam locomotive names (Union of South Africa, Trinidad and Tobago), these never found their linking narrative in the classroom.

But then what could our teachers have said? Empire was an uncomfortable subject. By the 1950s, an approach that stressed glorious conquest and the benefits of British rule was no longer tenable, and not only for moral reasons. What had been bloodily won was now being lost, usually peacefully but sometimes not, no matter that we would all be friends in the equitable-sounding Commonwealth. National decline would have been an unhappy theme in the classroom. Rather than this awkward mixture of past and present — one that might intimately involve us — it was safer to concentrate on the sufferings of the Paris commune.

How much this avoidance has to do with Britain’s present feelings towards its old empire is hard to know. No doubt the history curriculum has changed since my day and, in any case, feelings about the past come from many other sources than the classroom. But according to a YouGov poll conducted around the time of the Rhodes Must Fall protests two years ago, 43% of British people believed the British empire was a good thing and only 19% a bad thing, with 25% believing it was neither. Furthermore, 44% felt that Britain’s history of colonialism was something to be proud of and only 19% felt it should beregretted. As to the statue of Cecil Rhodes at Oriel College, Oxford, only 11% thought it should be removed.

These figures mock the plea made by Nigel Biggar , Oxford’s regius professor of moral and pastoral theology and canon of Christ Church, that we “moderate our post-imperial guilt”. According to YouGov, not even a fifth of us know such a feeling. It seems likely that Biggar’s real targets are not so much the guilty as the people he sees as the advocates of guilt, “the strident anti-colonialists [who] tell us ... that our imperial past was one long, unbroken litany of oppression, exploitation and self-deception”.

As it happens, many such people, or at least people who could be so caricatured, live next door to the professor in academia. Ever since his article, headlined “ Don’t feel guilty about our colonial history “, was published in the Times in late November, the hostility towards Biggar has been growing.

His first critics were Oxford’s anti-colonial student group, Common Ground; then 58 Oxford scholars who work on imperial and colonial history wrote to express their opposition; finally the protest spread across the world — it seemed to almost every institution where imperial history is studied — when another open letter, organised by an academic association called Scholars of Empire , attracted about 100 signatures. A few academics do support Biggar, but the most encouraging noises have come from letters and opinion pieces in the Times, the Telegraph and the Mail.

What alarmed Biggar’s detractors wasn’t so much the Times piece itself, which was written to support the views of an American political science professor, Bruce Gilley, whose piece titled “ The case for colonialism” had been recently published by Third World Quarterly, leading 15 out of 34 members of that journal’s editorial board to resign. Rather, their concern arose out of what the Times piece alerted them to — that Biggar had initiated a project called Ethics and Empire , which according to its website would scrutinise the proposition, common to “most reaches of academic discourse”, that “imperialism is wicked; and empire is therefore unethical”.

The project will run over five years and is held under the auspices of Oxford’s McDonald Centre, endowed by an American foundation, the McDonald Agape, whose rubric is “Encouraging distinguished scholars for Christ”. It makes sense, then, that a main objective is to develop “a nuanced and historically intelligent Christian ethic of empire” — though when I spoke to him this week, Biggar said he wondered if the word “Christian” was helpful. There are other concerns: the Oxford historian John Darwin resigned last month as the project’s co-leader, diminishing its historical authority; and looming above these local difficulties is the question of how empires are to be measured in terms of their behaviour and consequences, by what system and in whose eyes.

Biggar insists there will be nothing as crude as a balance sheet — “most cost-benefit analysis is merely prejudice masquerading as mathematics,” he has said. He wants “a far more intelligent and sophisticated way of evaluating empire morally”. But wanting and getting are two different things. To illustrate the complexities of empire, Biggar himself is always weighing one thing against another: the abolition of the slave trade versus the Amritsar massacre; the empire as the only armed resistance to the Nazis in 1940-41 (good) versus the extinction of indigenous Tasmanian people (bad). Gilley, the like-minded scholar Biggar admires, certainly believes in balance sheets when he describes how the colonial record might be assessed by measuring “development, security, governance, rights, etc” against the counterfactual: what would likely have happened in the absence of colonial rule.

Such arithmetic seems like madness: every historical fact, supposing it can be agreed on, has a thousand human ramifications. As well as that, there are the chasms that separate human experience. A topical example is Winston Churchill. Defending Rhodes in a speech at the Oxford Union two years ago, Biggar said: “If Rhodes must fall, so must Churchill, whose views on empire and race were much the same.” Or, you might say, even worse. Churchill had a visceral loathing of Indians. Hindus, he said to his private secretary in 1945, were a foul race “protected by their mere pullulation [rapid breeding] from the doom that is their due”.

How much his attitudes contributed to the Bengal famine of 1943 is arguable, but a persuasive case has been made (by the writer Madhusree Mukerjee, among others) that Churchill’s refusal to heed the advice of his Indian administration was instrumental in the death of between 2 and 3 million people.

The argument sits at the heart of a new documentary, Bengal Shadows . For every million Britons who know about the latest Churchill feature film, Darkest Hour , I suspect no more than half a dozen will know about the documentary (and the proportion in India may not be much larger). But what Churchill might mean to a resident of Midnapore, West Bengal, and another in Bognor Regis, West Sussex, could not be more different. Before we try to refine ethical approaches to the empire, we should perhaps try to discover more of what it was.

— Guardian News & Media Ltd

Ian Jack is a Guardian columnist