An international coalition of academics has condemned Oxford University’s support for plans to construct a balance sheet of the rights and wrongs of imperialism, with Oxford accused of backing apologists for Britain’s colonial legacy.

A letter signed by more than 170 scholars of empire from the UK, US, India, South Africa and other countries argue that the university is wrong to throw its backing behind a project named Ethics and Empire proposed by the university’s McDonald Centre.

The proposal has also been attacked as lacking academic credibility inside Oxford itself, with more than 50 fellows and researchers stating their opposition to the five-year interdisciplinary project headed by Nigel Biggar, a Regius professor of theology at Oxford.

The dispute reignites debate within Oxford about its historical baggage, with Biggar’s proposal referencing the recent controversy over the statue of Cecil Rhodes in Oriel College, which critics say memorialises Rhodes’s racism.

Biggar has dismissed criticism of his plans as “collective online bullying” and said the Ethics and Empire project “will pay careful attention to the historical variety of things that empire can be, and work out a more sophisticated way of evaluating them morally.”

But the signatories to the letter say they are dismayed at the project’s aims, which they say seek to “test the ethical critiques of empire against the historical facts of empire” and develop a “Christian ethic of empire”.

“The ‘balance sheet’ approach to empire is rooted in the self-serving justifications of imperial administrators, attempting to balance out the violence committed in the name of empire with its supposed benefits. It has long since lost its scholarly legitimacy,” the letter states.

“We are not surprised that such an approach should be recuperated by Prof Biggar – a long-time apologist for colonialism – but we are alarmed that the University of Oxford should invest resources in this project.”

Priyamvada Gopal, a reader in colonial and postcolonial literature at Cambridge University, who helped organise the letter, said: “It is our view that the Oxford project – scandalously endorsed by the university – is a highly selective and poisonous political agenda posing as a ‘dispassionate’ examination of the British imperial project.

“As the project’s own description makes clear, the aim here is to provide a rehabilitation of the British empire as largely a force for moral good, which in turn can be used to justify present-day military interventions.”

In response to earlier criticism, a spokesperson for the university said Biggar’s effort was a “valid, evidence-led academic project and Prof Biggar, who is an internationally recognised authority on the ethics of empire, is an entirely suitable person to lead it.”

Jon Wilson, a historian at Kings College London, said the international opposition was remarkable for its wide support among scholars of empire, with the signatures being gathered in less than 24 hours after Oxford issued its statement.

“Our concern is not with Prof Biggar, who can conduct whatever research he wishes, but the support his project has received from one of Britain’s leading universities,” Wilson said. “Any attempt to create a ‘balance sheet’ of the good and evil of empire can’t be based on rigorous scholarship. It’s disappointing Oxford is actively supporting something so flimsy and politically motivated.

“Every strand of research on the history of empire is united against this ill-conceived project. Scholars who don’t agree on anything else are agreed in their opposition to this.”

Among the signatories are the historian and screenwriter Alex von Tunzelmann, Prof Richard Rathbone of London’s School of Oriental and Asian Studies, and Prof Sarah Stockwell of King’s College London.

An Oxford student group named Common Ground, which aims to challenge racism and colonialism, also criticised the project and Biggar’s recent opinion article for the Times, headlined “Don’t feel guilty about our colonial history”.

Common Ground said: “The proud announcement of this project, following on the heels of Biggar’s article, reflects a university that has shown itself to be singularly incapable of reckoning with its colonial past.”