By Sally Hayden

LONDON (Thomson Reuters Foundation) - A hot meal. Dry clothes. A smile. Sometimes the first friendly face in months for hundreds of thousands of migrants who have come to Europe in the past two years is a volunteer aid worker.

Yet cases of sexual exploitation, human smuggling and involvement of pedophiles - revealed by volunteers and migrants in interviews with the Thomson Reuters Foundation - have prompted some charities and aid groups to call for background checks on new volunteers in largely unregulated situations.

For while criminal background checks are usually mandatory for people who work in charities or with children, the migrant crisis has sparked a wave of volunteers often acting on their own accord and with no oversight.

Emma Jarmaine, a British volunteer whose newly-formed non-profit A World of Hands runs various projects for refugees and asylum seekers, has been visiting Calais in France since last year.

"I think some of the volunteers have very blurred lines," she told the Thomson Reuters Foundation, adding that her organization was currently seeking charitable status.

"I've seen first hand volunteers getting stoned with refugees, getting intimate ... Obviously people are people and that happens but I think when that does happen it would probably make sense to remove yourself from the position of a volunteer."

The U.N. refugee agency, UNHCR, said it has "zero tolerance for this kind of behavior" while acknowledging that in many situations volunteers are the first people to be there to help.

"There are many volunteers across Europe doing important work (which is) one of the strongest manifestations of the public support and welcome for refugees," said UNHCR senior spokesman Andrej Mahecic.

But proper reporting of, and information sharing about any potential abuses is vital, he noted. A key principle of humanitarian work is to protect and safeguard the wellbeing of vulnerable people like refugees, he emphasized.

LACK OF EXPERIENCE

In interviews with the Thomson Reuters Foundation, volunteers and asylum seekers in France and Greece spoke of worries around unregulated volunteering including incidents of sexual exploitation and inadequate protection of children, which are leading them to call for proper background checks.

"We don't have enough organizations who know what they're doing," said British volunteer Sumita Shah, a manager in an accountancy body who has undergone training with British homeless charity Crisis.

Last month, she posted a six-page document offering guidance on safeguarding - a humanitarian aid term that denotes measures to protect vulnerable people - and on criminal background checks in an online group for volunteers on the Greek island of Lesbos.

The document advises organizations to establish codes of conduct and encourage volunteers to "report suspicions of abuse".

"Loads of people are just walking in and out," she said of the volunteering situation in Greece. "In the UK, that would never happen."

After a convicted British pedophile, Nathan Watson, was filmed on camera saying he planned to go to Calais to do "charity work" before being arrested by police in September, Shah checked all the online groups she moderates, and found he was in every one. That was a further wake-up call, she said.

Watson was jailed for 14 months after attempting to meet what he believed was a young girl for sex and placed on the sex offenders' register for 10 years.

When volunteers spot questionable behavior, Shah said they often message her as an online moderator to ask for advice but "it's really up to volunteers to regulate themselves on the ground".

She said calls for more stringent checks could put off some applicants.

"You've got to be safe but on the other hand if you put lots of bureaucracy in place, are you going to get enough people?" she said.

UNACCOMPANIED CHILDREN

One social worker who volunteered in the official Kare Tepe camp on Lesbos in September described the situation as "an absolute minefield".

"There are a huge amount of children away from their parents ... and loads of places where you could hide and not be seen," said the woman who declined to be named because she was not authorized to speak to the media.

Her organization had no child protection guidelines and no background checks on volunteers, she added.

Shah said volunteers have also supported some of the people-smuggling that has occurred. Volunteers in Greece sometimes give money to migrants or help them procure false identification documents, she said.

While they may be well intentioned, inexperienced volunteers may not be aware of the potential repercussions, including the consequences of helping fund criminal gangs, she added.

Meanwhile, both volunteers and migrants at the recently demolished Calais Jungle camp in France told the Thomson Reuters Foundation about sexual relationships between a small number of those giving and receiving aid – something major humanitarian groups forbid in their codes of conduct.

Marie-Elisabeth Ingres, who works on the Medicins Sans Frontiere's (MSF) migration desk in Paris, said it was forbidden to have sexual relations with "beneficiaries."

But she said with the high number of other volunteers who come from Britain and elsewhere it's "quite impossible" to keep track of those who aren't MSF-affiliated.

While unregulated volunteering raises many concerns, volunteers and migrants in Calais and Greece were keen to point out that the majority of those helping out in camps are well-intentioned and are trying hard to fill a humanitarian vacuum.

Amanda Whelan, a volunteer teacher who worked in Calais for several months, said the key problem was a lack of oversight while a large proportion of volunteers were young and lacked humanitarian experience.

"There's nobody telling you, you have to do this or can't do that. There's no organization overseeing the whole thing," she said. "Not everyone knows how they should be acting."

(Reporting by Sally Hayden, Editing by Megan Rowling and Belinda Goldsmith; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit www.trust.org)