In the first High Court challenge to the “one in, one out” scheme, the Eritrean man’s lawyers argued he needed more time to present evidence that he might have been the victim of modern-day slavery – and the decision to remove him had been rushed.
The injunction raises serious questions about whether other migrants allocated to flights will use the same grounds to delay or block their removal.
The Home Office is set to appeal against the decision and is reviewing the Modern Slavery Act to ensure it is not being misused.
Lawyers for the Home Office had argued that he could have claimed asylum in France. They added that delaying his departure could encourage others allocated to the return flights this week to make similar claims, and undermine the public interest in deterring lethal small boat crossings.
Mahmood said: “Migrants suddenly deciding that they are a modern slave on the eve of their removal, having never made such a claim before, make a mockery of our laws and this country’s generosity.
“I will fight to end vexatious, last-minute claims. I will robustly defend the British public’s priorities in any court. And I will do whatever it takes to secure our border.”