Workers at a charity founded by U2 singer Bono have been subjected to a 'toxic' culture of bullying and abuse.

Bosses at the ONE charity have covered up the horrific allegations for years, but a major Mail on Sunday investigation has exposed a catalogue of humiliating incidents that has now sparked a multi-million-pound lawsuit.

In the worst case, a married woman says she felt pressured to have sex with an elderly Tanzanian MP.

When she refused, she was demoted to receptionist and had her salary slashed, she claims.

Taken together, the astonishing complaints depict an organisation driven by intimidation and contempt, with staff belittled and undermined, both in front of colleagues and in public.

Workers at U2 singer Bono's ONE charity have been subjected to a horrific culture of bullying and abuse, a Mail on Sunday investigation has revealed

Much of the mistreatment is said to have been at the hands of Sipho Moyo (pictured in purple front row), the former £173,000-a-year Africa executive director of ONE

The charity also failed to pay taxes – despite campaigning against tax evasion – and is alleged to have illegally employed foreign workers on tourist visas.

Bono last night said he was 'deeply sorry' for the situation, which he admitted had 'gone badly wrong'.

He said he was left 'reeling and furious' about the scale of the allegations and vowed to meet victims to apologise in person.

Much of the mistreatment is said to have been at the hands of Sipho Moyo, the former £173,000-a-year Africa executive director of ONE. The complaints include claims that she:

Intimidated one member of staff into massaging her feet;

Woke another worker at 1am in South Africa and ordered her to sort out the air-conditioning in her hotel room – in Seattle;

Invited colleagues to parties at her house, only to use them as waiting staff, making one woman stand outside for up to seven hours mixing drinks;

Ordered a worker to find her a greyhound puppy, then drive to another city to collect it.

Pictured: Bono at a ONE campaign event in Philadelphia, USA

Moyo, the organisation's most senior African official from 2010 until 2015, hit back last night.

She said she 'vehemently denies' the bullying claims and argues she is being smeared.

She claims that other directors treated her 'like their personal maid' and abused her in public.

ONE, whose board of high-profile figures includes David Cameron and Facebook chief Sheryl Sandberg, now admits there was 'mistreatment and inaction' by former managers.

ONE (founder Bono pictured), whose board of high-profile figures includes David Cameron and Facebook chief Sheryl Sandberg, now admits there was 'mistreatment and inaction'

Bono (pictured) last night said he was 'deeply sorry' for the situation, which he admitted had 'gone badly wrong'

The charity rushed out a public statement nine hours after this newspaper sent it a long list of allegations.

Its current president, Gayle Smith, said she was 'troubled' by the claims, accepting there was 'what I would characterise as bullying and belittling of staff'.

The claims, backed by witness statements and documentary evidence, are hugely embarrassing for an organisation that harnesses celebrities to campaign against corruption, sexism and 'dirty money'.

VICTIM ONE: THE DEMOTED EXEC Sibu had been looking forward to her visit to Tanzania for the launch of an aid initiative. Yet as so often with her boss Sipho Moyo, it turned into a trial, with repeated accusations of incompetence and a humiliating public dressing-down. So after the trip, Sibu – then in her mid-30s and working in a senior ONE executive post – was relieved to be heading home to her family on January 16, 2015, as the pair waited in a private lounge at Julius Nyerere Airport. Then an older Tanzanian MP walked in and started chatting to Moyo in Kiswahili, which Sibu does not speak. Moyo suddenly introduced Sibu – not her real name – in English as her daughter. 'I was shocked when she said that – she hated my guts,' said Sibu. 'She said if he wanted to ask me out then he must run it past her. 'He started to laugh but I was so confused. He was maybe 60 years old. After that he came to me as if to shake my hand but held it for such a long time, making me very uncomfortable.' Sibu said that after asking why she was in Tanzania, and still clutching her hand, he joked about talking to her 'mother' since he wanted to see her again. 'My face changed, but Moyo said, 'Can you see how beautiful she is?' ' said Sibu. 'She was offering me to this guy.' She was distressed and kept looking desperately at Moyo – but insists the charity chief just looked back and remarked again on her beauty. 'I was not there to be beautiful but to work,' said Sibu. 'I did not know what to do. 'I was afraid to say anything – and I have never been afraid of a boss before. I was an object. And the person doing this to me was another woman.' Finally they boarded their plane. Sibu was seated across the aisle from the MP, who spent much of the four-hour flight asking if she was married and saying he had Moyo's blessing. 'I have no doubt I was being bartered, being offered for sex,' she said. 'I know about these things, I am a married woman.' Sibu kept silent, even crying at one point, but said Moyo just kept joking with the MP. 'It was the worst four hours of my life. When I landed, I left straight away.' Her story was confirmed by a colleague on the trip. 'She came to me distraught and I asked what happened,' he said. 'She told me, 'My boss is pimping me off with a politician.' ' Yet the ordeal was far from over. Sibu said Moyo warned her during the flight she would be fired if she refused to engage with the MP – and on February 12 this high-flying graduate was demoted to 'office assistant' with her salary slashed. She walked out and on March 13 won an uncontested arbitration for unfair dismissal. Yet Sibu said the incident, coming after months of abuse and bullying, destroyed her career, her confidence, her trust and ultimately her marriage. 'I still feel troubled. I used to be so bubbly, my life was rosy. Now I am haunted,' she said. 'I did not know I could be sold.' Sibu believes Moyo wanted to use her to win influence with the Tanzanian government. 'She wanted me to be her bait. It was so unethical, especially for ONE.' She says the group's relationship with the MP broke down after she refused to 'entertain' him. Moyo denied the allegations: 'They are a total fabrication. I said she was my daughter to protect her.' She added that if there was a demotion, it was through 'due process' and handled by the US office – which is confirmed by emails and the contract. Advertisement

'The toxic environment was terrible, with staff treated so badly,' said one former manager.

'It was awful for an organisation that claims to fight for social justice, respect and equality. I had never seen anything like this.

'This went on for years. It would never have been allowed to happen in London or Washington but we were just Africans. Their attitude was let them eat themselves.'

When a delegation was sent from London to dampen the disquiet, they told staff to rub a wooden elephant to channel 'negative energies'.

'This was the final insult,' said one man. 'It was really patronising. Did they think we were Africans so some voodoo would help?'

Pictured: Former Prime Minister David Cameron is among Bono's ONE charity backers

The scandal is another blow for the aid sector after revelations of sex parties and staff harassment at other major charities.

Angry ex-staff say their lives were left devastated after working in ONE's 'hostile environment' – and that nothing was done about their claims until after they started complaining publicly on social media in November in the wake of Hollywood sex scandals.

Last week lawyers acting for seven of the former staff, dismayed by inaction over the complaints, launched a legal case demanding £3.6 million compensation for distress.

They sent a letter seeking damages for 'emotional, physical and psychological abuse' under Moyo. Other staff said bullying continued for two years after she left.

Tom Hanks is also a supporter of Bono's ONE charity, exposed for a culture of bullying by the Mail on Sunday

The letter also alleges 'wrongful and malicious mistreatment' at the hands of Moyo, her former deputy director Nachilala Nkombo and Jane Ilori, a former human resources director, who they claim ignored their pleas for help.

Abuse and bullying led more than 20 staff to quit in five years, several saying they remain traumatised and in need of therapy. One British woman was treated for depression and her hair fell out due to stress.

The claims are a blow for Bono, who speaks about 'representing the poorest and most vulnerable people'.

VICTIM TWO: BRITISH MANAGER It was a big move for a single mother with a young autistic son, but Amahle was excited to move from the UK to join ONE's management team in Johannesburg in June 2012. Shortly before Amahle departed, Jamie Drummond, the charity's co-founder, warned her of 'problems' in the South Africa office. But brimming with confidence, Amahle (not her real name) assumed she would be OK. Instead she left the charity 18 months later a broken woman. She says she was on medication for depression, struggling to function with hair falling out from stress due to bullying – and feeling dreadfully guilty for the devastating impact on her son. Some incidents can sound small: being ordered to fetch her boss's bag each day, make tea in a particular way, or serve drinks at parties at Moyo's house. But the daily drip-drip of abuse, bullying phone calls, dealing with suppliers in tears after run-ins with her bosses, demeaning orders, public dressing-downs and shouting ground her down. 'It crushes you emotionally, mentally and physically,' she said. Yet she was trapped: ONE was not registered or paying tax in South Africa, so she had to work illegally on a tourist visa. This made it difficult to settle down or find another job. 'It was so hypocritical,' she said. 'But everything we spoke about was hypocritical. We were talking about female empowerment while they were breaking families.' She is especially angry that nothing was done despite complaints to head offices in London and Washington. 'The abuse was reported over and over again. Not one person within the organisation cared. 'If this had happened in the UK or US, heads would have rolled. But it was like we were meant to be grateful for having jobs. We were just black Africans.' Advertisement

He set up ONE in 2004 to raise awareness of poverty, backed by big aid charities. It has campaigned to write off Third World debt, has pushed anti-malaria campaigns and raised £360 million to fight HIV and AIDS through its RED offshoot.

Last night, the star said in response to the allegations: 'I hate bullying, can't stand it. The poorest people in the poorest places being bullied by their circumstance is the reason we set up ONE.'

The Mail on Sunday understands Mr Cameron was warned about the problems before joining the board three months ago, soon after the former employees started raising the matters on Twitter.

After being told the issue was in the past, he attended his first board meeting with Bono at Claridge's hotel in London.

The Charity Commission, however, was only informed 11 days ago. A spokeswoman said they were working to ensure that staff are 'properly protected'.

The issue started to emerge on November 7 last year when Idriss Nassah, a Malawian journalist, started tweeting about abuse and cover-ups during his year-long stint working in the communications department at ONE.

Facebook boss Sheryl Sandberg (pictured) is another of the ONE charity's celebrity backers

Other former workers responded with similar complaints. 'Don't remind me of that hellhole… my 4 months felt like a long prison sentence,' responded one.

After 17 people stepped forward, the group realised the scale of misery.

'I thought my experiences were bad but the more I talked with the others, the more I realised these problems were deep-rooted in the organisation,' said a former staffer.

The most serious allegation is that of the married woman in her mid-30s, who says she was demoted after refusing to sleep with a Tanzanian MP in his 60s.

Her claim is backed by a colleague who said the traumatised woman told him: 'My boss is pimping me off with a politician.'

However, Moyo told The Mail on Sunday that she 'doesn't recognise any element' of that claim.

BUILT BY A ROCK GOD, BACKED BY STARS AND NINE MILLION FANS: WHAT DOES ONE CHARITY DO? ONE was founded in 2004 by Bono and a couple of friends – Jamie Drummond, a former Christian Aid worker, and Bobby Shriver, a scion of the Kennedy family. It aims to harness the power of celebrity while raising cash from businesses to push the fight against poverty – and is a key plank in the Irish rock star's campaigning on development issues. The US-based organisation claims nine million members, based on email subscribers. And it has been backed by some of the world's top movie stars, including Brad Pitt, Tom Hanks and George Clooney, in its slick commercials. Funders include billionaires such as Bill Gates. The board features David Cameron, former US Treasury Secretary Larry Summers and Africa's richest person, Aliko Dangote. Perhaps this explains why it has held meetings in the five-star splendour of London's Claridge's Hotel – an unusual place for anti-poverty campaigners to press their cause. ONE runs campaigns against corruption and tax evasion – a 'trillion dollar scandal' for the developing world – although some board members are also executives of high-profile tax avoiders such as Facebook. Defenders point to the impressive £360 million its RED offshoot has raised for the fight against AIDS, TB and malaria through corporate partnerships. Like other aid organisations, it reels off statistics about improving healthcare and education in the developing world. Its highest-paid executive is RED's head Deborah Dugan, who was handed an annual package worth £414,344, according to its most recent tax filing. ONE's chief executive took home almost £350,000 in 2016. ONE preaches citizen activism. It seeks to make poverty history, attacks sexism and talks passionately about female empowerment. All of which makes these charges and claims of hypocrisy by its former African staff so devastating for its carefully constructed brand. Advertisement

Other staff recall a fusillade of angry phone calls into the night and at weekends. 'She would be screaming and shouting,' said one assistant. 'I stopped going to the movies or going out socially because the calls kept coming.'

Like others, she quit without having another job to go to. 'You ended up blaming yourself like a rape victim,' said one female manager.

'I've been a victim of this and you keep wondering what you could have done differently. It was a different kind of abuse but it still crushes you emotionally.'

Several say they have been left traumatised, lacking confidence and unable to hold down jobs, so want cash to fund therapy.

Staff allege they were forced to do endless menial tasks including, in one case, massaging Moyo's feet.

'I did not want to be shouted at again so if massaging her feet meant no shouting, then I did that,' said the woman. Moyo denies the claim.

Another told of being ordered to fix the heating at a conference Moyo was attending abroad, despite being in South Africa – only to eventually discover that Moyo was sitting next to the event organiser. 'It was so humiliating,' she said.

Actor George Clooney has appeared in TV adverts for Bono's ONE charity

Several disclosed they had to spend nights serving food and drink at Moyo's parties. Moyo insists they were invited as guests, but one email to staff tells them not to 'interact' with real guests.

'I thought I was invited to a dinner party,' said one executive. 'But I was made to stand outside in heels for six or seven hours as a waitress. I did not even know how to mix drinks. I don't drink – it's against my religion.'

Moyo insisted last night she was tough but fair. 'I treated ONE staff like my family,' she said.

'I demanded high standards but never treated people in a disrespectful form.' She believes she is being 'framed' for wider failings in ONE to make everything look like the fault of Africans, claiming: 'Being an African at ONE is to be inferior.'

Moyo – who went on to be chief of staff for the president of the African Development Bank – also confirmed that ONE did not pay tax on its employees' salaries, saying it was a decision taken in Washington.

Bobby Shriver (pictured) was one of Bono's friends who helped establish the ONE charity

A former member of staff revealed ONE was not registered in South Africa, which meant payroll taxes were ignored, and staff struggled to fix pensions, buy homes or lease cars as 'you need tax clearance to do anything'.

Another ex-staffer said: 'I was paid from an American bank account and no taxes were taken from my salary.'

The arrangement also meant employees were flouting the law by working under visas that said they were tourists.

One woman told of crossing the border into Zimbabwe every three months to renew her documents.

ONE says it was acting as a nonresident taxpayer at the time.

Staff fury over the bullying is compounded by claims it was ignored despite repeated complaints to senior figures in London and Washington. 'Image is everything to ONE,' said one woman.

An email sent to trustees in February 2015 by a departing manager highlighted a workplace that was 'toxic, unprofessional and dominated by fear, intimidation and bullying'.

BONO'S STATEMENT IN FULL We are all deeply sorry. I hate bullying, can't stand it. The poorest people in the poorest places being bullied by their circumstance is the reason we set up ONE. So to discover last November that there were serious and multiple allegations of bullying in our office in Johannesburg left me and the ONE board reeling and furious. You question the whole reason you're doing this. My team and I heard concerns about low morale and poor management in this office but nothing along the lines of what emerged recently. I was assured that those concerns were being dealt with – clearly, they were not. I'm thankful that Gayle Smith, ONE's new chief executive (former US Agency for International Development boss), has taken swift and decisive action to address what had gone badly wrong. Although the bullying allegations centre on an individual (an accomplished female executive formerly of the African Development Bank and the World Bank), the head office failed to protect those employees and I need to take some responsibility for that. In fact, if they would agree, I would like to meet them and apologise in person. While ONE isn't funded by governments or the public, we should still uphold the highest standards the public would expect. Advertisement

Among those receiving the email was Bono's assistant, but sources claim the star is 'furious' the complaint was not passed on to him.

Former staff say high turnover and cases taken to arbitration should have rung alarm bells.

Three days after Nassah mentioned the issues, ONE's general counsel Brian Healy sent a circular claiming the charity did not tolerate 'any sort of harassing, bullying or discriminatory behaviour'.

One week later, an official from ONE's Washington office flew to meet the complainants in Johannesburg.

A former manager broke down in tears entering the office, so strong were the bad memories. This is when the former staff were urged to rub the wooden elephant.

In January, Gayle Smith, a former aide to Barack Obama who became ONE's president two years ago, said she was 'appalled' by the allegations and admitted 'mistreatment and inaction' by former management.

Actor Brad Pitt is among the famous faces who back Bono's ONE charity

An internal inquiry accepted there was 'unprofessional conduct' and a 'wholly inadequate' response. But the former employees were only offered careers advice.

Following The Mail on Sunday approach, Ms Smith insisted a new management team set up an independent inquiry as soon as the allegations surfaced last November.

But the ex-staff behind the legal claim said: 'ONE is only making a public admission after becoming aware of The Mail on Sunday investigation – just like they only took any action when we went public about their abuse and bullying on social media.

'It is all about ONE trying to look good, but never sincerely addressing and compensating the victims of its years of rampant abuse.'

Ms Nkombo is now Zambia country director for WWF. The wildlife charity said references were checked before her appointment and 'no allegations came to light'.

She was unavailable for comment last night.