Shamima Begum's lawyer quits before launching sensational attack on court case

It was taken from her in 2015, when as a schoolgirl, she fled to Syria to join the terrorist organisation.

McCullough served as her special advocate – a barrister who acts for a client in a case where information is being kept secret from them.

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Due to national security concerns, the special advocate cannot communicate with the client or their usual lawyer after seeing the evidence.

McCullough, who appeared most recently as last week to represent Begum, said that the secret hearings were unfair and imbalanced towards defendants.

He said that disparities were "being aggravated by sustained neglect of the special advocate system".

McCullough criticised rules which prevents special advocates from having direct contact with their clients once the evidence had been laid bare.

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He said that the "basic principles of fairness and the rule of law require the unfairness associated with closed material proceedings to be minimised".

The KC said that he decided to quit because of the Government’s failure to uphold its promises concerning the secret proceedings.

He said that ministers had failed to respond to an independent review of the system by Sir Duncan Ousesly, a retired High Court judge.

McCullough called out the structure of the system as being unfair and said the Government was not giving enough support to lawyers who take on the cases.

In a statement on the review, McCullough said that ministers had been pushed for a reply and that it was "hard to see how any of the 20 recommendations could be controversial in principle … yet, the Government has given no public indication of its response, let alone a commitment to implementing anything from the Ouseley report".

The Isis bride has claimed to be a victim of human trafficking whilst she was in Syria.

Her lawyers have begun a bid to overturn the decision which stripped her of her British citizenship.

Samantha Knights KC argued: "The appellant's trafficking was a mandatory, relevant consideration in determining whether it was conducive to the public good and proportionate to deprive her of citizenship, but it was not considered by the Home Office.

"As a consequence, the deprivation decision was unlawful."