The government should not select judges on the basis of their political views as they do in the US, the outgoing president of the supreme court, Lady Hale, has warned.

Speaking at a ceremony to mark her retirement as she approaches the age of 75, the first woman to lead the UK’s highest court made a direct intervention in the debate about the dividing line between politics and the law.

In the aftermath of the government losing two landmark, Brexit-related judgments at the supreme court – over article 50 and the prorogation of parliament – there have been calls from Brexiter lawyers and MPs for the appointment of judges to be approved by the Commons and for them to avoid making political judgments.

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Defending the independence of the judiciary, Hale declared of her fellow justices: “They are so open-minded and so unpredictable. We go into our post-hearing deliberations not knowing what the others are going to say. Well sometimes. We do not know one another’s political opinions – although occasionally we may have a good guess – and long may that remain so.

“Judges have not been appointed for party political reasons in this country since at least the second world war. We do not want to turn into the supreme court of the United States – whether in powers or in process of appointment. On the other hand, we do have an idea of one another’s approach to judging and to the law. But we are often surprised. Everyone is persuadable.”

In 2012, the House of Lords constitution committee investigated and rejected proposals for US-style confirmation hearings to endorse the selection of supreme court justices. “In order to ensure judges continue to have appropriate independence from parliament,” the committee said, “judicial candidates should not be subject to US-style pre or post-appointment parliamentary hearings. Political considerations would undoubtedly influence both the parliamentarians chosen to sit on the panels and the questions put to candidates.”

In her address, Lady Hale also said that during her time on the bench she had been described as: “‘The most ideological, politically correct judge ever to have been appointed’ – and a ‘hardline feminist’ apparently intent on destroying the institution of marriage – and that was all because I had suggested that marriage was such a good thing that some of its benefits should be extended to the unmarried. Those same commentators didn’t notice later when I defended the institution of marriage...”