Migrants take food and support from charity workers before insulting them in the next breath, he said.
Charity employees have seen first hand the desperation and devastation of the migrant crisis caused by record numbers of people displaced from the Middle East and Africa.
Since June 2015 the millions of asylum seekers fleeing Syria, Iraq, Afghanistan and Africa have had a huge impact on European member states who have opened their doors to them.
The humanitarian effort is huge with thousands of charities working across Europe to feed, help and direct them.
However, speaking frankly about integration and resettlement, one aid worker warned European nations, and Britain in particular, must handle immigration with a firm hand.
The aid worker from Serbia, who asked to remain anonymous and has worked on the crisis in the Balkans, speaks Arabic and is often mistaken for a Muslim.
Because of this he has been able to hear and understand scathing remarks made against aid workers providing help to refugees.
These include the charity workers being branded “filthy Christian kuffars” – a derogatory Arabic word meaning non-believer.
Now, the aid worker has warned European countries to get tough or face the consequences.
He said: “The difference is I know these people, I hear them. I’m sorry, I have to say it, I hear what they say when they speak to their own people – not what they say in English.
“I am not saying don’t take them, I am saying your country needs to be strong, get tough.
“What happens is you let them build mosques and you let them practice their religion and then what? They don’t want to live by your rules. “You don’t know what is going on in mosques.
“You have to make it happen or it won’t be your country anymore. They have no intention of living under Christian law.”