that his legal advice declared the Withdrawal agreement's backstop protocol would mean the UK being indefinitely locked into a customs union with the EU if future negotiations collapse and that the only way the UK could leave the Backstop would be the signing of a future trade deal which could take many years to complete. The former Brexit Secretary Dominic Raab and three serving Cabinet members confirmed the contents of the letter to the Sunday Times. In February 2019, Theresa May placed Cox in charge of negotiating changes to the Northern Ireland backstop in the EU withdrawal agreement. On 24 September 2019, the Supreme Court of the United Kingdom ruled unanimously that Prime Minister Boris Johnson's prorogation of parliament was unlawful, overturning the High Court's judgment, given by the Lord Chief Justice, in the government's favour. On the same day, minutes of a conference call between cabinet ministers (which included Cox) were leaked to Sky News. The minutes of the call, which took place after the prorogation had been approved by the Queen, detailed that Cox briefly told the cabinet at that time that in his view the prorogation was lawful and constitutional and that any accusations of unlawfulness "were motivated by political considerations". Cox's full advice to the Government has not been published, as per precedent to protect government legal advice being prone to influence. The next day Cox appeared in the House of Commons to answer an urgent question on the Government's legal advice and on the implications of the Supreme Court's decision. Cox rebutted calls for him to resign and criticisms of the Government's position, stating that senior and distinguished judges had agreed with the Government's view that the issue was not justiciable and chiding MPs for refusing to agree to a means of the UK leaving the EU while repeatedly preventing the House of Commons from dissolving for an election. In February 2020, Cox said the public is concerned about the creeping "judicialisation of politics" and said people were right to worry that unelected officials were making decisions that ought to be taken by Parliament. He promised there would not be radical reforms. He stated his opposition to the highly politicised US selection process of Supreme Court and suggested he preferred the Canadian system. Cox said that "there's a case for looking at how supreme court judges are appointed... There's a committee of the Canadian parliament