On the surface, at least, Yamen Alahmad was a model refugee, a Syrian teenager apparently motivated only by the hope of starting a new life far from the hell of his homeland.

Last week, however, Germany’s anti-terrorism police kicked in the door to the flat the state had granted him in the northern city of Schwerin. The officers had evidence that Alahmad was building a bomb.

As if more evidence were needed of the terrorist threat facing Europe, the 19-year-old had arrived in Germany as an unaccompanied minor at the peak of the migrant crisis in 2015, becoming one of the country’s 1.6m registered asylum seekers.

He was charged with terrorism. Over the internet he had ordered electronic and chemical materials used in bomb making