Boris Johnson has said more work needs to be done to tackle “very serious issues” of racism in Britain as ministers faced a backlash over a Government-backed review on racial disparity.

The Prime Minister thanked Samuel Kasumu, his most senior black adviser, after it emerged he had quit, with Downing Street insisting his departure was “absolutely nothing to do” with the report.

The landmark review by the Commission on Race and Ethnic Disparities (Cred) drew heavy criticism over its findings, with claims that it is culturally deaf, out of step with public opinion, and “steeped in denial”.

Its chairman said it had found no evidence of “institutional racism”, and the report criticised the way the term has been applied, saying it should not be used as a “catch-all” phrase for any microaggression.

During a visit to Middlesbrough on Thursday, the Prime Minister called the review a “very interesting piece of work” but admitted more needed to be done to address racism.

“I don’t say the Government is going to agree with absolutely everything in it, but it has some original and stimulating work in it that I think people need to read and to consider,” Mr Johnson said.

“There are very serious issues that our society faces to do with racism that we need to address.

“We’ve got to do more to fix it, we need to understand the severity of the problem, and we’re going to be looking at all the ideas that they have put forward, and we’ll be making our response.”

Mr Johnson defended the commissioners for coming forward “with about 24 interesting ideas to promote equality” and said ministers would respond to the findings “in due course”.

Mr Kasumu resigned from his role as a special adviser to Mr Johnson on civil society but will stay in post until May to continue work on improving vaccine uptake in minority groups, Politico reported.

Asked about Mr Kasumu’s resignation, Mr Johnson said: “I worked very closely with Samuel in the last year or so and he’s done some great stuff.

“I thank him very much, particularly on helping to encourage vaccine take-up amongst more hesitant groups and communities.”

Downing Street sources insisted Mr Kasumu’s departure was “absolutely nothing to do with the report”, which was published in full on Wednesday.

Politico reported that Mr Kasumu notified the Prime Minister’s chief of staff, Dan Rosenfield, of his decision to quit his job – which paid up to £75,000 – last week.

He has reportedly been unhappy in Government for some time, with a resignation letter drafted – but then retracted – in February.

In the letter, which was obtained by the BBC, he accused the Conservative Party of pursuing “a politics steeped in division” and suggested the Equalities Minister, Kemi Badenoch, may have broken the ministerial code in her public spat with a journalist.

Shadow women and equalities secretary, Marsha de Cordova, said: “To have your most senior adviser on ethnic minorities quit as you publish a so-called landmark report on race in the UK is telling of how far removed the Tories are from the everyday lived experiences of black, Asian and ethnic minority people.

“Their divisive report appears to glorify slavery and suggests that institutional racism does not exist, despite the evidence to the contrary. It is no wonder they are losing the expertise from their team.”

The commission said in the report that geography, family influence, socio-economic background, culture and religion all affect life chances more than racism.

Its findings have been described as insulting and divisive, and the chairman of the review has been accused of putting a “positive spin on slavery and empire” when explaining its recommendation on teaching history in schools.

The report proposes a Making Of Modern Britain teaching resource to “tell the multiple, nuanced stories of the contributions made by different groups that have made this country the one it is today”.

In commission chairman Dr Tony Sewell’s foreword to the report, he said the recommendation is the body’s response to “negative calls for decolonising the curriculum”.

He wrote that the 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.”

Highlighting the passage on Twitter, Ms de Cordova said it was “one of the worst bits” of the report which was “putting a positive spin on slavery and empire”.

Dr Sewell defended the commission against the accusations in a statement on Thursday, saying that to suggest it was “trying to downplay the evil of the slave trade” is “absurd”.

Halima Begum, chief executive of race equality think tank, the Runnymede Trust, said: “Comments about the slave trade being a Caribbean experience, as though it’s some kind of holiday… this is how deafening it is, cultural deafness, it’s completely out of kilter with where British society is, I believe.”