A proposal to allow some 9,000 young Afghan migrants to stay in Sweden has been controversial among voters, as a new report shows that at least 78 per cent are really adults.

Last month, Swedish Prime Minister Stefan Löfven and his government announced a plan to allow some 9,000 “underage” Afghan migrants to stay in the country after a wave of protest against deportations to Afghanistan.

The issue has remained a highly controversial topic ahead of this year’s national election, but now it has been revealed that the vast majority of the migrants were not underage Expressen reports.

The newspaper conducted a study with a portion of the 9,000 migrants and found that none of the men had valid identification documents when they entered Sweden and that a significant number, almost half, had lived in Iran for at least a year before heading to the Scandinavian country.

Additionally, 99.4 per cent of them are male.

86 Per Cent of Recently Tested ‘Underage’ Migrants in Sweden Are Actually Adults https://t.co/DX9UW4Xu6Y — Breitbart London (@BreitbartLondon) July 7, 2017

According to Anna Lindblad, a lawyer and legal expert at the Swedish Migration Board, the agency lists many migrants as 18 at the time of their asylum decision if they cannot prove they are under 18.

Lindblad said that in some cases, where is it obvious the migrant in question is an adult, their claims of being a minor are dismissed — but in other cases, migrants are required to prove they are underage, and 7,000 of the 9,000 were unable to convince the agency they were not adults.

The revelation follows medical tests done by the Swedish government that have repeatedly shown that a majority of migrants claiming to be underage were adults.

Migration has been voted the most important election issue in Sweden ahead of the September elections, according to a study conducted by Demoskop.

The populist anti-mass migration Sweden Democrats have become the party most favoured by Swedish voters on the topic, with leader Jimmie Åkesson decisively winning a debate on the subject with several other party leaders.

Follow the debate, a new poll from YouGov revealed a surge in support for the Sweden Democrats with them tied for first place alongside the ruling Social Democrats.