A former Oxfam employee has said she encountered allegations of rape, harassment and sex in exchange for aid handouts when she was working for the charity.

It comes as the President of Haiti hit out at the allegations of sexual misconduct by aid workers, calling it a "serious violation of human dignity" after claims Oxfam workers used prostitutes while delivering aid to the country in 2011.

The charity has been given until the end of the week to explain how it will handle further allegations.

In an interview with Channel 4 News the former head of global safeguarding at Oxfam, Helen Evans, said during her time with the charity she was told about two women being coerced to have sex and a worker who had failed to disclose he had previously been struck off for sex abuse.

"There was a woman being coerced to have sex in a humanitarian response by another aid worker," she said.

"[There was] another case where a woman had been coerced to have sex in exchange for aid and another one where it had come to our attention that a member of staff had been struck off for sexual abuse and hadn't disclosed that, and we were then concerned about what he might be doing," she said.

Ms Evans revealed that she told the charity that there was a need for more resources to tackle the number of allegations.

It comes as the Charity Commission prepares to launch a statutory inquiry into Oxfam.

The charity's deputy chief executive, Penny Lawrence, resigned on Monday over claims its employees sexually exploited victims of the 2010 Haitian earthquake and hired prostitutes for sex at homes funded by the charity in Chad in 2006.

Upon her resignation Ms Lawrence said she took "full responsibility" for the behaviour of its staff in Chad and Haiti.

In a statement she said: "I am desperately sorry for the harm and distress that this [misconduct] has caused to Oxfam's supporters, the wider development sector and most of all the vulnerable people who trusted us."

Mark Goldring, Oxfam's CEO said: "I deeply respect Penny's decision to accept personal responsibility. Like us, she is appalled at what happened and is determined to do what is best for Oxfam and the people we exist to help."

In an interview with ITV News on Saturday he denied Oxfam had lied to the government in 2011 over sex claims about its workers.

International Development Secretary Penny Mordaunt said her department would set up a dedicated unit to "urgently review safeguarding across all parts of the aid sector".

That could include setting up a global register of aid workers in order to "guard against criminal and predatory individuals being re-employed by charities and abusing again".

While Oxfam investigated the allegations of misconduct in 2011 and told the Department for International Development it had dismissed a number of its employees, it failed to report the allegations were about sexual misconduct towards the charity's beneficiaries.

Now it faces an inquiry by the Charity Commission over concerns it may not have "fully and frankly disclosed" all the details of the allegations in Haiti.

Responding to the allegations the President of Haiti, Jovenel Moise, tweeted: "What happened with Oxfam in Haiti is an extremely serious violation of human dignity.

"There is nothing more outrageous and dishonest than a sexual predator who uses his position as part of the humanitarian response to a natural disaster to exploit needy people in their moments of greatest vulnerability."

Now the spotlight is being shone on other charities, with Save the Children, Christian Aid and the British Red Cross all confirming they have dealt with cases of sexual abuse or harassment by staff in the past 12 months.