The global development secretary has said the government will end funding to Oxfam unless the charity shows "moral leadership" and hands over all its information on its aid workers' apparent use of prostitutes in Haiti.
The British government is reviewing its relationship with Oxfam amid a deepening sexual misconduct scandal involving some of the charity's employees working in Haiti after its devastating 2010 quake.
"The way this appalling abuse of vulnerable people was dealt with raises serious questions that Oxfam must answer".
"Our approach to this matter would have been different had the full details that have been reported been disclosed to us at the time", the Charity Commission said in a statement.
Oxfam staff have raised concerns over recruitment policies following allegations that the aid charity covered up a sex scandal in Haiti in 2011, Oxfam says, as a new report claims Oxfam staff were involved in a similar scandal in Chad.
She confirmed the charity would meet with the Department for International Development (DFID) on Monday and the Charity Commission, which regulates the sector, later this week. It said Oxfam's investigation into the charges was hampered by a "determination to keep it out of the public eye".
The allegation that Oxfam has not fully cooperated with regulators and donors has sparked outrage in Britain.
"But I don't think it was in anyone's best interest to be describing the details of the behaviour in a way that was actually going to draw extreme attention to it".
More than 120 workers for British charities were accused of sexual abuse in the past year alone, sparking fears overseas aid organisations are being are being targeted by paedophiles.
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Women believed to be sex workers were reportedly invited to the Oxfam team house on a number of occasions.
Everybody - the 25,000 staff and volunteers - are compromised by this, the hundreds of thousands of people who support Oxfam every month are compromised by this, and to everybody I apologise, he said.
It said van Hauwermeiren resigned from Oxfam in 2011, after admitting that prostitutes had visited his villa in Haiti.
The French charity told AFP it made pre-employment checks with Oxfam but that the UK-based organisation "did not share with us the reasons for his resignation as head of mission in Haiti or the results of its internal inquiry".
Reuters could not independently verify the allegations contained in The Times report and was unable to reach any of the Oxfam staff who worked in Haiti.
On Saturday, Oxfam was forced to deny further reports that it gave positive references to those it dismissed.
And there was also nothing to stop them from getting former or current staff to provide a reference "in a personal capacity", she said.
But the charity said it had publicly announced an investigation into the allegations when they surfaced in 2011.
Oxfam said four members of staff were dismissed and three, including the country director, were allowed to resign before the end of the investigation.