To cut a long story short, the EU outsourced the protection of its border to Turkey.
Before the 2016 deal refugees were flooding into the EU through Greece. Turkey kindly agreed (for €s) to police a safe zone in Norther Syria, which would mean the refugees would be safe and didn’t need to ‘invade’ the EU.
But the Turks aren’t getting much help, and have only been given half the money they were promised. So they are saying, they might not bother, and just let the refugees stream into the EU. Turkey do not want these people either.
Being in or out of the EU will not make the slightest bit of difference. We did not sign up to the Schengen Area, so we can stop them (if we can catch them).
// Under a 2016 agreement with the EU, Turkey imposed stronger controls to curb the flow of migrants and refugees to Europe.
The deal involved an EU pledge to provide €6bn (£5.4bn; $6.6bn) in aid to Turkey to house Syrian refugees.
Mr Erdogan complained that only €3bn of that had arrived so far //