Trustees of the charity Samaritans are in talks over the future of their new CEO after a Guardian investigation revealed claims that the Alzheimer’s Society paid out as much as £750,000 to staff who signed non-disclosure agreements (NDAs) during his tenure there.

Jeremy Hughes is due to take over at Samaritans in May. But after claims about the payouts emerged alongside allegations that he displayed bullying behaviour to junior employees during his time as chief executive of the Alzheimer’s Society, a Samaritans spokesperson said on Monday: “Our board of trustees takes this issue extremely seriously and are currently in discussions about the situation.”

The news comes as two more former employees of the Alzheimer’s Society came forward to say that they had received settlements and signed NDAs after complaining about discrimination and bullying.

The two, who said their mistreatment took its toll on their mental health, decided to break their agreements to speak out following the Guardian’s report detailing concerns raised about the dementia charity in a complaint submitted to the charity watchdog.

One told the Guardian: “I think the Samaritans need to review their decision to appoint Hughes and do their own investigation, because the mismanagement that happened under his watch at the Alzheimer’s Society is his responsibility. He ran the charity as an old boys’ club.”

Last week the Guardian revealed the existence of an 11-page whistleblower complaint, made to the Charity Commission in February 2018, which warned the NDAs could be seen as an attempt to silence staff at the Alzheimer’s Society. Insiders at the society claim it has been beset by allegations of bullying and a toxic management culture.

Despite the serious nature of the allegation that hundreds of thousands of pounds had been spent to “silence” staff who signed NDAs, the watchdog did nothing to investigate the complaint – an oversight it now admits was a mistake.

Separately, an ex-senior staff member said Hughes had an “explosive temper” and displayed bullying behaviour towards staff, including shouting and undermining them.

The Alzheimer’s Society disputed the £750,000 payout figure and said the charity had “zero tolerance of bullying and discrimination”. In an internal email sent by its chief operating officer, Kathryn Smith, to staff on Monday, Hughes – who is still in post as the society’s CEO – was quoted as saying: “I am deeply concerned by the allegations. I have always been determined to ensure everyone at the Alzheimer’s Society has a positive working experience. Everything I do is in order to make the biggest difference for people affected by dementia.”

Asked on Monday to respond to criticism of Hughes, a Samaritans spokesperson said: “Samaritans appointed Jeremy Hughes following a rigorous recruitment and selection process. The welfare of our staff and volunteers within a positive, inclusive working culture at Samaritans is of the utmost importance and our board of trustees takes allegations of this nature very seriously.”

The spokesperson said the board was in discussions in response to a further question about whether Hughes would take up his new role.

One of the whistleblowers at the Alzheimer’s Society, who signed an NDA and received a settlement after complaining about being discriminated against, spoke of a “consuming” and “toxic culture” at the charity that made them dread going into work every day.

“I was under enormous stress and this was affecting my emotional health at work and at home,” they said. “The Alzheimer’s Society might claim that they have a robust internal complaints and whistleblowing policy which protects the employee, but I know from first-hand experience that this is not the case.

“If you are brave enough to make a formal complaint and put your head above the parapet, you have sealed your fate and most likely the end of your career at the charity.”

They added: “The usage of NDAs to silence former employees is abhorrent. The Alzheimer’s Society relies predominantly on public funding and for this reason it is so important that these facts are out in the open so that supporters can make informed decisions on who they donate their money to. Hughes must take full responsibility for the toxic, discriminatory and bullying culture that was created across the organisation.”

A second former employee of the charity, who also received a settlement and signed an NDA after complaining about being bullied, said: “Jeremy Hughes is accountable for the culture within the organisation. He’s at the helm and was aware of what was going on. But he did not stop it. He’s even accused of bullying behaviour himself.

“Those are not the qualities of someone leading any charity, not least the Samaritans, which deals daily with people with serious mental health issues. What about the mental health of staff at the Alzheimer’s Society?

“What I went through had an impact on my mental health and I’m not the only one. The Samaritans should rethink his appointment.”

The Alzheimer’s Society says the £750,000 figure for settlements is inaccurate. It declined to give its own sum. It said it only used settlements for “legitimate reasons”. The charity’s director of people and organisational development, Corinne Mills, said: “We are deeply concerned about the experience of the two ex-employees quoted. All complaints raised with us are taken very seriously and investigated thoroughly.

“A review of our anonymous staff engagement survey shows that the number of people reporting issues was low even in comparison with the charity sector, but we’re always working to reduce this further.

“We have dedicated employees and volunteers who support people affected by dementia and we are always looking to improve the experience they have. We have zero tolerance of bullying and discrimination – our evidence shows we have not and do not use settlement agreements or non-disclosure agreements to stop anyone reporting any whistleblowing, harassment or discrimination complaints.”

• Footnote added on 30 May 2020: On 4 May 2020 the Charity Commission reported on the outcome of its regulatory case involving the Alzheimer’s Society, finding “no evidence that confidentiality clauses used by the charity were designed to or would have had the effect of preventing staff from reporting any whistleblowing, bullying, harassment or discrimination complaint. Allegations reported in the national media around the amount of money paid out in settlements were not substantiated by the evidence the Commission saw.” See press release here.

The article was also amended on 30 May 2020 to better reflect the terms in which the Alzheimer’s Society disputed the alleged figure for settlements.