Labour has been dragged into the High Court by pro-migrant human rights lawyers over Shabana Mahmood's "unlawful" one-in, one-out deal with France.
Legal challenges have been brought against the Government by six migrants - three of whom have already been sent back to France - who claim to be victims of human trafficking.
The group are challenging the legality of how they were treated under the Home Secretary's scheme.
If their claims are upheld, Ms Mahmood could be significantly hindered in the number of migrants she would be able to deport in exchange for other asylum seekers in France.
In September, the Home Secretary altered guidance on modern slavery in a bid to fast-track deportations under the terms of the deal.
The previous guidance enabled migrants who had seen their claims turned down by the Home Office appeal the decision prior to their deportation from Britain.
But under the changes, they are not able to launch a challenge, and must instead apply for support once in France.
Now, Sam Grodzinski KC - representing the six migrants - has argued that Labour's changes to the guidance breached human rights and are illegal.
Labour has been dragged into the High Court by pro-migrant human rights lawyers over Shabana Mahmood's 'unlawful' one-in, one-out deal
|GETTY
The barrister said that a lawful system is one that “identifies the paramount importance of identifying victims [of trafficking] correctly” and the Home Secretary's policy was an “institutional disregard of potentially relevant evidence”.
Mr Grodzinski told Justice Sheldon the move infringed upon the European Convention on Human Rights (ECHR) and the Council of Europe Convention on Action against Trafficking (ECAT).
He said the migrants have "have a fundamental right under ECAT to have their claims properly investigated".
The human rights lawyer cited Home Office data from last year which showed that almost 80 per cent of modern slavery rejections were overturned.
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If their claims are upheld, Ms Mahmood could be significantly hindered in the number of migrants she would be able to deport
| GETTYHe also argued that migrants arriving into Britain do not give their full trafficking history when questioned upon arrival because they do not understand what they are being asked.
The barrister told the court: "Victim identification is a process that takes time; it can’t be done speedily, not if it is to be done properly."
The Home Office has said that in exceptional cases, migrants are able to apply for reconsideration prior to their deportation.
But Mr Grodzinksi told Justice Sheldon that this was not made clear to caseworkers in guidance and it only occurred when legal cases were under threat.
The Home Office has said that in exceptional cases, migrants are able to apply for reconsideration prior to their deportation
| GETTYLast month, the Home Secretary's overhaul of Britain's asylum system was met with fury from around 100 Labour backbenchers, who penned a letter to her urging the Government to reconsider.
Tony Vaughan MP - who coordinated the correspondence - wrote: "We can change our immigration system for the better without forgetting who we are as a Labour Party.
"You don’t win back public confidence in the asylum system by threatening to forcibly remove refugees who have lived here lawfully for 15 or 20 years.
"That just breeds insecurity and fractured communities," he added.
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