More than 15% of refugees travelling north through the Horn of Africa were kidnapped during their journey last year, according to what is believed to be one of the most comprehensive surveys of migration journeys.

Researchers from the Mixed Migration Centre (MMC), who conducted 11,150 interviews across 20 countries and seven migration routes, warned that kidnappings may be increasing and identified people travelling through the Horn of Africa to north Africa and Europe as the most vulnerable.

While previous reports have highlighted the issue of refugee kidnappings, most of the information was anecdotal. This is the first large survey to provide percentage figures. The research will inform policy responses on the ground, and contribute to the development of a dashboard system to forecast future migration patterns.

Bram Frouws, head of the MMC, which is part of the Danish Refugee Council, said the hardening of borders had left people even more vulnerable to abuse by smugglers, who often work alongside or with tacit permission from state officials.

“Usually, families receive a phone call from kidnappers saying they have their family member and demanding a ransom. Sometimes they can hear the voice or even the torture happening on the phone to force them to pay,” said Frouws. Ransoms are often about $2,000 (£1,570).

It is possible that smugglers are increasingly turning to kidnapping as they look for alternative sources of income because of the decreasing number of people travelling through certain routes, he added.

“As numbers are going down – at least the number arriving in Europe is going down – as a result of attempts to stop or control this migration, this means there are fewer clients for smugglers,” Frouws said. “Maybe some of them are earning less or being pushed out of business. This could be a way to make it up.”

Almost all the victims are held with the threat of or actual use of violence, and most are physically restrained.

The research showed that, while travelling through the Horn of Africa, some nationalities are much more vulnerable than others. Almost one in five of the 1,200 Ethiopians interviewed said they had been kidnapped at least once during their journey.

Of the 288 Sudanese people interviewed along the same route, 4% said they had been kidnapped. Researchers believe this may be because most kidnappings take place in the Sudan, and that Sudanese people might be better at circumventing the risks, or that they might be starting their journeys beyond the most dangerous areas.

Researchers surveyed people as they passed through key migration hubs between May 2017 and September 2018. The sample is not representative because there is little concrete data on the absolute numbers of people on the move worldwide, but researchers say the findings are indicative of the horrific abuses suffered by many.

Across all migration routes, 615 people reported that they had been kidnapped at least once.

Researchers found the second most dangerous route was from Afghanistan to Europe, where around 8% of people reported they had been kidnapped at some stage along their journey.

Frouws said the dehumanisation of refugees by politicians or the media was making it easier for smugglers to carry out such crimes.

“The more they are dehumanised, there’s less and less outrage over this kind of inhumane treatment,” said Frouws. “Media articles talking about tides of migrants, waves of migrants, migrants streaming into Britain – all of this really dehumanises people and presents migration as something that is really out of control.”

Last week, the home secretary, Sajid Javid, appeared to suggest that he would make it harder for people to seek asylum, a right enshrined in international law, in order to deter people from crossing the Channel. He was also criticised for repeatedly referring to people making the Channel crossing as “illegal” migrants. It is not against the law to seek asylum.