Champion said: "If you are a woman in a humanitarian crisis desperate to get food for your children and the person standing there who is able to give you that food says 'you can have the food, but this is what I want in exchange', who wouldn't do that for their children?
"How would you know that that wasn't the rate of negotiation to get that food for your children?
"I've heard across different humanitarian crises that there's almost a known exchange rate. If you want the aid, if you want a tarpaulin, then your child needs to be made available, if you want a job then you are expected to sleep with the person who's able to give you that job."
The MP said she had heard evidence from the Democratic Republic of Congo that "it was so normal that women were expected to have sex for jobs" that translators were "negotiating the deal" between them and UN officials.
She said charities needed to follow the example of the Catholic Church in facing up to and addressing years of abuse within their organisations.
Abuse known about for decades
The Sexual Exploitation of Women and Children by Aid Workers conference was told the abuse had been known about for more than two decades.
But despite focus on the sector in the wake of the Oxfam sexual abuse scandal, new research by King's College has found that under-reporting and "cover-up by officials" have contributed to the fact that its true extent is not known.
Jessica Toale, who carried out the literature review, found data from the UN since 2017 "shows that allegations against UN staff, related personnel and implementing partners is consistently higher than those against the military and police contingents of peacekeeping missions".
Research from Liberia estimated that, at the height of the humanitarian crisis, about 58,000 women had engaged in transactional sex with UN workers, she said.
About 60 per cent of the perpetrators had been identified as local staff or contractors, the study found.
Toale said: "Sexual exploitation is more prevalent than sexual abuse, and this most often takes the form of exchanging food for sex for food and basic items including sanitary pads, tarpaulins for shelter or employment opportunities."
But she warned there was no consistency to the data or obligation on NGOs to publish reports of abuse.
'Vested interest' in not investigating
Asmita Naik, a former UN worker turned consultant, said the "reason we know so little" is that "there is a vested interest in not looking into this amongst the very type of groups that would normally be profiling human rights issues".
Her concern that there was a "moral assumption" that peacekeepers are "doing good" was backed by Champion, who said there was not enough safeguarding as it is assumed that those on the ground are "doing it for all the right reasons".
Champion called on the UK Government to do more to ensure transparency and protect whistleblowers because many of the NGOs are funded with taxpayers' money and "we have an absolute duty to make sure that it is spent in the most appropriate way".
Britain's Foreign, Commonwealth and Development Office has already made any transactional sex by its workers a gross misconduct issue, but is under pressure to ensure the same rules apply to all organisations that receive Government money.
