The EBU also found further gangs across Europe using the hawala system for criminal activity. One former money launderer previously involved in European hawala networks, whom we are calling Frank, told the EBU he had been involved in transactions totalling several hundred million euros.

His first introduction to the hawala system had been at an office in a small town outside Rotterdam, he said. There, five or six messengers had arrived with money in about an hour and a half, transferring at least a million euros, he estimated.

“What I found out later is that it’s not just about money. It’s about the financing of terror. It’s about drug trafficking. It’s about prostitution and all sorts of other crap, to put it nicely,” he said.

Cases in Austria have also revealed how the hawala system is bound up with people smuggling and violence.

In one case investigated by Austrian broadcaster ORF, part of the EBU network, Austrian police raided what they called “the biggest hawala office in Vienna”. It was run from a kebab restaurant on a busy thoroughfare and which authorities say was used to make payments for people smuggling.

Two Syrian brothers who ran the operation were charged with human trafficking, as well as torturing and raping a courier who had lost €350,000 (£300,000), saying he had been robbed. They were convicted last year and sentenced to 18 and 8 years in prison respectively.

Austrian police and Europol also recently dismantled another people-smuggling ring financed through hawala, which officials said had transported about 100,000 people into Europe over 18 months.

Gerald Tatzgern, who leads human-trafficking investigations at Austria’s Criminal Intelligence Service, the BK, told ORF that torture was a reality of people smuggling and was also used to maximise profits.

He said: “Videos of the torture are then sent to the families, saying that if they don’t send another €1,000 or several thousand euros, then the person concerned – your son, your brother, your father – will suffer.”