Donald Trump is a “racist” who has used the “N-word” repeatedly, Omarosa Manigault Newman, once the most prominent African American in the White House, claims in a searing memoir.

The future US president was caught on mic uttering the taboo racial slur “multiple times” during the making of his reality TV show The Apprentice and there is a tape to prove it, according to Manigault Newman, citing three unnamed sources.

Mr Trump has been haunted from around the time of his election in 2016 by allegations that outtakes from the reality TV show exist in which he is heard saying the N-word and using other offensive language.

In her book, Unhinged, to be published next week, the former Apprentice participant insists that the reports are true, although she does not say she heard him use the word herself.

She also claims that she personally witnessed Mr Trump use racial epithets about the White House counsellor Kellyanne Conway’s husband George Conway, who is half Filipino. “Would you look at this George Conway article?” she quotes the president as saying. “F**ing FLIP! Disloyal! F**king Goo-goo.”

Both flip and goo-goo are terms of racial abuse for Filipinos.

Critics have previously questioned Ms Manigault Newman’s credibility and are likely to accuse her of seeking revenge against the administration after her abrupt dismissal last December.

At the time, she writes, she felt a “growing realisation that Donald Trump was indeed a racist, a bigot and a misogynist. My certainty about the N-word tape and his frequent uses of that word were the top of a high mountain of truly appalling things I’d experienced with him, during the last two years in particular”.

High ratings Recalling her sudden and unceremonious departure, she writes: “It had finally sunk in that the person I’d thought I’d known so well for so long was actually a racist. Using the N-word was not just the way he talks but, more disturbing, it was how he thought of me and African Americans as a whole.”

His insurgent election campaign was rocked in October 2016 by the release of an Access Hollywood tape in which he bragged about grabbing women “by the pussy”. The media firestorm prompted Bill Pruitt, a producer on the first two seasons of The Apprentice, to tweet that there were “far worse” tapes of Mr Trump behind the scenes of the show.

Further allegations emerged that Mr Trump had used the N-word in the recordings. Then, following the New York property tycoon’s shock victory over Hillary Clinton, the actor and comedian Tom Arnold claimed to have the video of Mr Trump using racist language.

“I have the outtakes to The Apprentice where he says every bad thing ever, every offensive, racist thing ever,” Arnold told the Seattle-based radio station Kiro. “It was him sitting in that chair saying the N-word, saying the C-word, calling his son a retard, just being so mean to his own children.”

But Metro-Goldwyn-Mayer, which owns the rights to the reality TV show, and its British creator, Mark Burnett, have resisted pressure to release the footage because of “various contractual and legal requirements”.

Once close to Mr Trump, Ms Manigault Newman was among his most high-profile supporters during the election campaign and drew a top salary of $179,700 as director of communications for the White House office of public liaison. She held her April 2017 wedding at Mr Trump’s luxury hotel, close to the White House.

Hers is the second memoir from a former Trump administration member, following that of the ex-press secretary Sean Spicer, but it was always expected to be less adulatory. This week the Daily Beast reported that she had secretly recorded conversations with the president and “leveraged” this while seeking a book deal. On Sunday she is due to appear on NBC’s flagship political show Meet the Press.

White House Some commentators have struck a note of scepticism about her book. Brian Stelter, senior media correspondent at CNN, wrote in an email newsletter: “Is former ‘Apprentice’ star Omarosa Manigault-Newman a reliable source of info about the Trump White House? Buckle up for debates about that in the coming week. Because she’s about to betray Trump in a new tell-all book.”

For its part, the White House has previously dismissed criticisms from her. In February the deputy press secretary, Raj Shah, said: “Omarosa was fired three times on The Apprentice and this was the fourth time we let her go. She had limited contact with the president while here. She has no contact now.”

In the book, she recalls how in late 2016 Mr Trump’s team held a conference call and scrambled for how to respond to the tape but it never came out. Then a source from The Apprentice contacted her and claimed to be in possession of it. Mr Trump was in office and Ms Manigault Newman continued to investigate.

She continues: “By that point, three sources in three separate conversations had described the contents of this tape. They all told me that President Trump hadn’t just dropped a single N-word bomb. He’d said it multiple times throughout the show’s taping during off-camera outtakes, particularly during the first season of The Apprentice.”

Recalling that she appeared on the first season, MS Manigault Newman reflects: “I would look like the biggest imbecile alive for supporting a man who used that word.” She says she confided in the former White House communications director Hope Hicks, who said, “I need to hear it for myself,” and continued to ask her frequently about what progress she was making.

She believes that MS Hicks told the White House chief of staff, John Kelly, that MS Manigault Newman was close to getting her hands on the tape, and this gave him cause to terminate her job, though he found a different pretext.

Damning passage Four months after her departure, she spoke by phone to one of her Apprentice sources. “I was told exactly what Donald Trump said – yes, the N-word and others in a classic Trump-goes-nuclear rant – and when he’s said them. During production he was miked, and there is definitely an audio track.”

Ms Manigault Newman also recalls her interactions with Mr Trump during the filming of The Celebrity Apprentice in late 2007 – a time when the little known Democrat Barack Obama was in the ascendent. “During boardroom outtakes, Donald talked about Obama often. He hated him. He never explained why, but now I believe it was because Obama was black.”

In another damning passage, she describes his “broken outlook” and how “the bricks in his racist wall kept getting higher”, wondering if he did “want to start a race war”. She adds: “The only other explanation was that his mental state was so deteriorated that the filter between the worst impulses of his mind and his mouth were completely gone.”

The book comes days after Mr Trump faced renewed allegations of racism over his persistent descriptions of the congresswoman Maxine Waters as having a “low IQ” and CNN journalist Don Lemon as “the dumbest man on television”, as well as criticism of the basketball star LeBron James. This weekend marks the first anniversary of the white supremacist march in Charlottesville, Virginia, that erupted in deadly violence; the president claimed there were “very fine people on both sides”.

Elsewhere in Unhinged, published by Gallery Books, an imprint of Simon & Schuster, Ms Manigault Newman takes aim at Mr Trump’s sexism. Recalling more outtakes from The Apprentice, she says he asked personal questions about female contestants such as “What do you think she’s like in bed?” and “Do you think she’s sexy?” He allegedly asked male contestants: “Who you think would be better in bed between the two of them?”