Former British Prime Minister David Cameron speaks at a conference in Las Vegas. File picture: Richard Brian/Reuters

London - David Cameron knew last year about ‘toxic’ abuse and bullying allegations at U2 singer Bono’s charity, on whose board he sits.

The former prime minister was briefed about the claims when he attended his first board meeting of the charity ONE with Bono at Claridge’s Hotel in December.

Bono, who founded ONE to fight poverty in Africa, said on Sunday he was left ‘reeling and furious’.

The abuse allegations include claims that a married female charity worker was demoted for refusing to have sex with an elderly Tanzanian MP.

The claims are embarrassing for the singer, who set up ONE in 2004. Its supporters include Hollywood stars Brad Pitt, Tom Hanks and George Clooney, and it has received funding from Microsoft billionaire Bill Gates.

Bono said he was ‘deeply sorry’ for bullying allegations between 2011 and 2015 in ONE’s Johannesburg office.

These centred on former executive director Sipho Moyo, who is alleged to have made staff massage her feet and hired workers on tourist visas to dodge tax, even though the charity campaigns against tax evasion.

The scandal, which is the latest to rock the charity sector, emerged on Sunday after staff began complaining on social media in the wake of Hollywood sex scandals.

Seven ex-staff are claiming £3.6million in compensation for ‘emotional, physical and psychological abuse’ under Miss Moyo.

Read: Bono charity faces lawsuit over 'toxic' culture of bullying and abuse

Even though Mr Cameron was told about the scandal three months ago, the Charity Commission was only informed 12 days ago, and has begun investigating.

Mr Cameron was assured that the allegations of ‘bullying and belittling of staff’, and ‘sexist and suggestive comments’ were historic when he took up the post.

But whistleblowers suggested Sunday that the scandal extended beyond a single director, claiming 20 bullied staff quit.

Idriss Ali Nassah, who was the first to tweet about abuse after working in ONE’s communications office, said: ‘For years @ONECampaign – all the way to the President and CEO – knew of the abuses. It enabled the abuses. It tolerated them. It looked the other way. It didn’t care.’

Staff member Suri Tsholetsane tweeted that ONE ‘provided an enabling environment for abusers to practice their pathetic acts’.

Read more: Bono apologises after shocking claims of abuse at his charity

Miss Moyo is accused of pressuring a married woman to ‘become intimate’ with a foreign official. When she refused, she was apparently demoted to receptionist and had her salary slashed, telling colleagues: ‘My boss is pimping me off with a politician.’ The former £173,000-a-year Africa executive director is said to have told a worker to find her a greyhound puppy and drive to another city to collect it. She also allegedly woke staff at 1am in South Africa to make them sort out the air-conditioning in her US hotel room.

One ex-manager said: ‘The toxic environment was terrible. This went on for years. It would never have been allowed to happen in London or Washington but we were just Africans.’ In February 2015 an email was sent to trustees and Bono’s assistant by a manager telling of a workplace ‘dominated by fear’. But sources claim it was not passed to the star.

On Sunday, Bono said: ‘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 need to take some responsibility for that.’

Also read: ‘Bono charity boss pimped me off to politician’

Miss Moyo, who was the organisation’s most senior African official from 2010 until 2015, ‘vehemently’ denied the bullying claims on Facebook on Sunday.

She said they ‘appear to be designed to discredit the massive successes made during my tenure’, telling The Mail On Sunday she was 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.’

A spokesman for David Cameron said: ‘He has full confidence in the organisation’s new leadership and the steps taken to thoroughly investigate and address these reports with urgency.’

Warned of toxic workplace: David Cameron and Bono. Right: Sipho Moyo, who faces accusations