Twenty eight percent of Save the Children UK employees say they have experienced either discrimination or harassment in the past three years, an independent review has found.

The review, commissioned by Save the Children in the wake of sexual harassment scandals, warned the charity must do more to build trust in its investigation processes.

The survey, which involved close to 700 staff at Save the Children, found the most common complaint was of people’s opinions being ignored, though others reported being humiliated, ridiculed or being the target of spontaneous anger.

There were also “a small number of incidents of gender harassment and unwanted sexual attention”. About seven in 10 staff members took part in the survey.

The report found that the charity’s whistleblowing policy lacked independence and responsiveness, adding: “We do not believe the present arrangements offer a reliable route to anonymous disclosure, nor a source of independent advice, support, advocacy and challenge.”

The review, led by Suzanne Shale, a visiting professor at University College London, was set up following allegations that Save the Children had failed to investigate sexual abuse and inappropriate behaviour by senior staff members. Both Justin Forsyth, its former chief executive, and Brendan Cox, the former policy director and widower of the MP Jo Cox, left the charity in 2015 following allegations of misconduct.

After leaving Save the Children, Forsyth went on to a senior role at Unicef. He resigned in February this year after the reports of inappropriate behaviour emerged, saying that he did not want coverage of his past to damage charities. Cox also resigned from the charities More in Common and the Jo Cox Foundation, set up in the aftermath of his wife’s murder.

The review said there were a small number of examples of gender harassment since 2015, which included disparaging comments about pregnancy, child-rearing responsibilities, and a woman’s personal demeanour or appearance.

Examples of unwanted sexual attention outlined in the report included sexual innuendo, sexualised remarks, intrusive questions about personal life and unwelcome touching in areas such as the waist.

The report said that rates of workplace incivility or bullying in the charity may be similar to public sector organisations such as the NHS and the civil service. But it added the charity must do more to promote social and ethnic diversity, especially among its board of trustees.

Kevin Watkins, chief executive of Save the Children, said in a statement: “There have been failures in our organisational culture and processes, including widely reported historic cases in which there were abuses of power and authority.

“To the women affected, I unreservedly and unconditionally apologise on behalf of Save the Children. It must never happen again.”

The charity would act on the review’s findings, he said, adding that all staff would be consulted on a new plan to improve working culture. This plan is to be independently monitored over the long term.

Alexia Pepper de Caires, a former Save the Children employee and whistleblower, said she did not believe the report would spark a culture change, and that she was not invited to take part in the review.

“They’re inane recommendations, I’ve seen them before. There were various processes going on when I was there in 2014 and 2015. The culture then was recognised to be unsustainable,” she said.

“We’re looking for accountability for what was going on in the first place, which was that a very small number of men knew what was going on and were allowed to police it themselves.”

Save the Children said that all women who made complaints were contacted and invited to take part in the review.

The Charity Commission is separately investigating Save the Children’s handling of the allegations against its senior staff.