A pivotal deal to staunch the flow of migrants from Turkey into the EU, masterminded by German chancellor Angela Merkel, was thrown into doubt yesterday after the resignation of Turkey’s pro-European prime minister.

Ahmet Davutoglu, who personally negotiated the deal with Ms Merkel, quit following a power struggle with President Recep Tayyip Erdogan. The premier’s departure imperils an agreement credited with sharply reducing the influx of asylum-seekers into the EU — and rescuing Ms Merkel from a potentially fatal political backlash.

The deal enables the EU to send migrants arriving illegally on the Greek islands back to Turkey in exchange for an easing of visa requirements on Turkish visitors and financial aid. However, Mr Erdogan has responded coolly to the agreement and has shown increasing hostility towards the EU.