Lord Sumption, an outspoken figure who served on the court from 2012 to 2018, told The Guardian in a new interview that he “thought — and I still think — that the conduct of Israel in Gaza is grossly disproportionate”.

He was one of three former UK Supreme Court justices who signed a letter in April 2024 which called for an immediate suspension of UK arms sales to Israel, alongside former president Baroness Hale of Richmond and Lord Wilson.

Lord Sumption said genocidal intent is “quite a difficult thing to establish” but he had read the provisional decision of the International Court of Justice in the proceedings brought by South Africa against Israel “and it seemed to me that they were saying that that was an arguable proposition”.

On the arms sales letter, he added: “Given that the obligation of parties to the Genocide Convention is proactively to prevent it happening and not just to react after the event, I thought that the authors of the letter — and I wasn’t the draftsman — had got a point.”

The former judge went on to say he thought supporters of Palestine “have had a rough time in a number of European jurisdictions, notably Germany, where there’s been direct — and government — moves to suppress that strand of thought altogether”.

He claimed the UK “haven’t got anywhere near as close to things as that”, but acknowledged that there had been calls for “toughness on pro-Palestine demonstrations, which assume, without actually saying, that it’s perfectly obvious that support for Palestine is wrong”.

“I don’t think it’s wrong,” he added.

Lord Sumption’s new book, The Challenges of Democracy: And the Rule of Law, is to be published by Profile Books on Thursday.