Video report by ITV News Correspondent Angus Walker
An Oxfam worker who was sacked over sexual misconduct allegations in Haiti was later re-hired by the charity in Ethiopia.
The charity described the decision to employ Gurpreet Singh as a consultant in the African nation as a "serious error".
Several staff were sacked or resigned in 2011 over a string of lurid claims, including that they had used prostitutes while delivering aid to Haiti.
Oxfam said in a statement it had identified that hiring the man "even in an emergency as a short-term consultant" was a "serious error and should never have happened".
It continued: "We are still checking how this occurred but it further highlights that we need an organisation and sector-wide approach to the vetting and recruitment of both staff and consultants, especially in emergencies where there is pressure to fill posts quickly in order to help save lives."
The charity is now investigating whether there were "any issues" while the man was posted in Ethiopia.
It is the latest revelation in a scandal which has seen the renowned aid charity rocked by a crisis of credibilty.
The man at the centre of the Oxfam scandal - a former director in Haiti - says there are a number of "lies and exaggerations" in stories regarding the claims surrounding his use of prostitutes.
Roland van Hauwermeiren, who quit his role with Oxfam 2011 after being accused of using sex workers while working in Haiti as part of a relief effort following an earthquake in the country, has spoken for the first time about the events.
“A lot of people, including the international media, will feel blushes on their cheeks when they hear my version of the facts,” Roland van Hauwermeiren told Belgian newspaper Het Nieuwsblad.
Mr van Hauwermeiren admitted certain details that had come to light were accurate.
"It is not that I deny everything. There are things that are described correctly. But there are many lies and exaggerations.
"Parties every week? Fancy villas? Women paid with money from the organisation?"
He also appeared on Belgium television admitting he made mistakes and had sex with Haitian women but claimed to be in a relationship with them: "I see nothing wrong with that, I admit with hindsight I should have acted differently and should have known better, I should have been smarter," he said.
Roland van Hauwermeiren moved to another charity in Bangladesh after resigning from Oxfam which claimed not to have been warned about the nature of his departure.
"The Archbishop is deeply disappointed by allegations of immorality and possible criminality involving humanitarian workers linked to the charity," a statement from his office said.
The retired church leader was also saddened that the allegations would tarnish the good work achieved by many thousands of people working for Oxfam, it added.
Simon Pegg however told ITV News he will not be withdrawing his support for the charity.
"Oxfam is an organisation which helps countless people. I think it would be wrong to hold the entire organisation to account for the actions of a few people. I worry about the people that are going to suffer if everybody abandons this charity," the actor said.
He added: "All I know is that Oxfam are dealing with it as best they can.
"This isn't something that was done by Oxfam this was done by morally reprehensible people who managed to infiltrate Oxfam."
Meanwhile, Oxfam said that it was "too early to tell the impact of the crisis" on donations, but revealed 1,270 people cancelled their direct debits between Saturday and Monday - almost double the average of 600 cancellations per month.
A spokeswoman added: "We are extremely grateful to all those who continue to support us, those who have made additional gifts, and those who have sent messages of support.
"They are determined that the millions of people that Oxfam helps worldwide every year don't suffer as a result of the actions of a few."
Oxfam also said it sacked its Haiti country director last year following allegations of "mismanagement" and "inappropriate behaviour".
But the charity stressed the dismissal of Damien Berrendorf, who served as the Oxfam's country director in Haiti from 2012 to 2017, was "not related to sexual misconduct" and was "not connected to the case in 2011".