More than 40 prominent broadcasters, celebrities and actors of colour have condemned the BBC, demanding it reconsider a decision partially upholding a complaint against the presenter Naga Munchetty, calling it “deeply flawed, illegal and contrary to the spirit and purpose of public broadcasting”.

In a letter published in the Guardian, the actors Lenny Henry, Adrian Lester and David Harewood, and presenters Krishnan Guru-Murthy and Gillian Joseph are among signatories describing the decision as “racially discriminatory treatment”.

It follows a backlash against the corporation on social media after the BBC Breakfast host Munchetty was found to have breached the corporation’s editorial guidelines following criticism of Donald Trump for telling politicians of colour to “go home”.

Munchetty’s co-host, Dan Walker, had asked her opinion after Trump tweeted in July that four congresswomen should “go back to the totally broken and crime-infested places from which they came”. All four were people of colour, with only one born outside of the US.

In response to Walker’s question, Munchetty said: “Every time I have been told, as a woman of colour, to go back to where I came from, that was embedded in racism.” She added that she was “absolutely furious a man in that position thinks it’s OK to skirt the lines by using language like that”.

The BBC said Trump’s remarks were widely condemned as racist, and Munchetty was entitled to give her personal response. However, its editorial complaints unit (ECU) found she had breached editorial guidelines because BBC journalists were not allowed to “give their opinions about the individual making the remarks or their motives for doing so”.

Facebook Twitter Pinterest Signatories to the letter include (left to right): Adrian Lester, Afua Hirsch, Gina Yashere, Lenny Henry and Krishnan Guru-Murthy. Photograph: PA

The letter to the BBC on Friday warns the decision will have a “profound effect on the future diversity within the BBC”.

It says requiring BAME broadcasters to remain “impartial” about how they feel about their experiences of racism is “ludicrous” and that to require them to “endorse racism as a legitimate ‘opinion’ is an abrogation of responsibility of the most serious nature”.

The consequences of the decision are “widespread with implications for the entire media landscape in the UK”, it says. The scope of its effect, the signatories say, is already evident in the “unprecedented number of BAME media figures who have openly and publicly voiced their condemnation”.

The letter states that the ECU “does not reflect the diverse cultural views in the BAME communities in the UK”, and that it should address its own levels of diversity.

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It calls on BBC management to support journalists and acknowledge there can be no expectation of impartiality over expressions and experiences of racism.

It says the ECU ruling failed to acknowledge that “racism is not a valid opinion on which an ‘impartial’ stance can or should be maintained”. For those who experience racist abuse, including Munchetty, “being expected to treat racist ideas as potentially valid has devastating and maybe illegal consequences” and is contrary to race equality and human rights legislation, it says.

“To suggest a journalist can ‘talk about her own experiences of racism’ while withholding a critique on the author of racism (in this case President Trump) has the ludicrous implication that such racism may be legitimate and should be contemplated as such,” it adds.

The letter’s signatories, who also include the broadcaster and writer Afua Hirsch and the science journalist Angela Saini, say that BBC journalists have contacted them privately to express concern about the “climate of fear” at the organisation and concerns over the consequences of their speaking out in support of the statement.

Among those who have also backed the presenter are the chancellor, Sajid Javid, who called the decision “ridiculous” and added that Munchetty’s reaction was “perfectly understandable”.