Video report by ITV News Correspondent Juliet Bremner
The former Oxfam worker at the centre of the Haiti sex scandal had previously quit another charity after a similar incident, the whistleblower who exposed him has told ITV News.
Paul Hardcastle, who worked with Roland van Hauwermeiren at charity Merlin, alleged the Belgian had been dismissed after the second Liberian Civil War in 2004 for having charity workers ferry him to nightclubs to pick up women.
Hardcastle, Merlin's then-programme coordinator for Liberia, claimed van Hauwermeiren had and other senior staff ran a charity-funded "party house" for girls in the capital Monrovia and that exploitation was "rife" in the country.
Van Hauwermeiren was allowed to resign from Merlin and went on to become Oxfam's head of staff during the Haiti crisis in 2010.
He quit Oxfam in 2011, rather than be held to criminal account for his actions, after he and other workers were alleged to have paid local prostitutes for sex.
It comes as International Development Secretary Penny Mordaunt revealed she would be meeting with National Crime Agency bosses on Thursday over Oxfam's handling of the Haiti scandal.
Mr Hardcastle claimed that Merlin's country management team in Liberia, of which van Huawermeiren was the director of, would abuse the charity's assets to chase women.
"Their team house was a party house, basically, for girls and which ran most evenings," Mr Hardcastle told ITV News.
"They would meet for dinner in the evenings which would be outside the team house, and then after dinner they would go to the nightclubs with the drivers and the Merlin-stickered cars, and they would pull women from the nightclubs and then go back to the team house with them."
Mr Hardcastle said when he brought the issue up with van Hauwermeiren the Belgian fired him.
"I reported it directly to the country director, Roland Van Hauwermeiran, because he was in charge of the whole operation, and at that point he said that he would dismiss me, because I was out of control as it were and he was the boss," Mr Hardcastle said.
"And they had the power to do that, they have incredible power these guys. So he dismissed me."
Mr Hardcastle alerted Merlin's head office in London of the incident and when he got back to the UK he gave the head office a debrief of what he had experienced.
He said Merlin sent out two senior members from the head office to Monrovia to investigate, leading to him being reinstated in his position and van Hauwermeiren and two other Merlin staff being dismissed.
"What amazed me is that this had been going on for such a long time but no-one had dealt with or reported it before," he said.
"And I think that's the whole picture of aid work that people in the field are very frightened with their program coordinators, who have ultimate power."
Mr Hardcastle said he was "horrified" to find out van Hauwermeiren had been allowed to take up a position at Oxfam in 2006.
"I didn't know that at the time, but what I find horrifying is that the human relations department didn't stop him from going further, that he was allowed to go and join big organisations like Oxfam without them checking up on him and his work."
Yesterday Oxfam announced a package of new measures to "strengthen the prevention and handling of sexual abuse cases".
Caroline Thomson, Oxfam's GB chair of trustees, said in a statement that she shared "the anger and shame" the reports had generated.
"It is clear that such behaviour is completely outside our values and should never be tolerated," she said.
Ms Thomson added: "We apologise unreservedly. We have made big improvements since 2011 and today I commit that we will improve further."
Oxfam said it would bolster its safeguarding policies including through the introduction of an independent consultant to help "drive out unacceptable behaviour".