Human rights experts from the United Nations have alleged that a government-commissioned race report tried to "normalise white supremacy".
The UN Working Group of Experts on People of African Descent said it "categorically rejects and condemns" the findings of the Commission on Race and Ethnic Disparities.
The report, which was published last month, said racism remained a "real force" but Britain was no longer a country where the "system is deliberately rigged against ethnic minorities".
Commission chairman Dr Tony Sewell said it had found no evidence of "institutional racism".
And its report criticised the way the term has been used, saying it should not be applied as a "catch-all" phrase for any microaggression.
But the UN's human rights experts laid into the report, saying in a statement released by the UN Human Rights Office of the High Commissioner: "In 2021, it is stunning to read a report on race and ethnicity that repackages racist tropes and stereotypes into fact, twisting data and misapplying statistics and studies into conclusory findings and ad hominem attacks on people of African descent."
They urged the government to reject the findings, adding: "The report cites dubious evidence to make claims that rationalise white supremacy by using the familiar arguments that have always justified racial hierarchy.
"This attempt to normalise white supremacy despite considerable research and evidence of institutional racism is an unfortunate sidestepping of the opportunity to acknowledge the atrocities of the past and the contributions of all in order to move forward."
The commission's report attracted criticism when it was published, including accusations that it was "putting a positive spin on slavery and empire".
In the foreword, Dr Sewell said a teaching resource should look at the influence of the UK during its empire period and how "Britishness influenced the Commonwealth" and how local communities influenced "modern Britain".
He added: "There is a new story about the Caribbean experience which speaks to the slave period not only being about profit and suffering but how culturally African people transformed themselves into a remodelled African/Britain."
In response to the criticism at the time, the commission said suggestions it would downplay the atrocities of slavery was "as absurd as it is offensive".
And one of its authors, space scientist Dr Maggie Aderin-Pocock, said people criticising the report were being "insulting" and taking it out of context.
The UN experts also hit out at what it said was the report's "mythical representation of enslavement is an attempt to sanitise the history of the trade in enslaved Africans".
They urged the government to make sure there is an "accurate reflection of historical facts", adding: "The distortion and falsification of these historic facts may license further racism, the promotion of negative racial stereotypes, and racial discrimination."
A spokesperson for the commission said the UN experts had "grossly misrepresented the report's findings, and appears to be a response to negative press coverage rather than the substance of its content".
They added: "The misleading claims they have made risk fostering division on the subject of race, rather than constructive discussion on the issues."
Downing Street also rejected the UN's criticism, with Boris Johnson's spokesman saying: "Our view is that this report misrepresents the findings.
"We remain proud of the UK's long history as a human rights champion and we encourage everyone to read the original report in full."
Asked about the panel's claim that the report could "normalise white supremacy", the Number 10 spokesman replied: "Absolutely not.
"This report in no way condones racist behaviour and in fact it highlights that racism and inequality are still problems for our country."