In response to a question from Keir Starmer, Sunak listed a series of issues that he said showed the Labour leader making about-turns, ending with a quip about his stance on “defining a woman, although in fairness, that was only 99% of a U-turn."

His remark was intended to embarrass Starmer, who Sunak's Conservatives have accused of vacillating on the issue of self-identification, and who have pounced on his comment last year that “99.9% of women haven't got a penis.”

Starmer, who had welcomed the mother of Brianna Ghey, Esther Ghey, was visibly furious in response. He said the comments were inappropriate, and Sunak later acknowledged Ghey.

“Of all the weeks to say that, when Brianna's mother is in this chamber. Shame,” Starmer said. “Parading as a man of integrity when he's got absolutely no responsibility.”

Last Friday, the two 16-year-old convicted murderers of Brianna a year ago were handed life sentences with minimum prison terms of 20 and 22 years. The horrific murder shocked the nation. Brianna, who was 16, was stabbed with a hunting knife 28 times in her head, neck, chest and back in broad daylight after being lured to a park in the town of Warrington in northwest England on Feb. 11, 2023.

Brianna's mother has been widely praised for her dignified response, calling for the families of the convicted pair to be shown some empathy and compassion. In an interview Sunday with the BBC, she said she would be open to meeting the mother of Scarlett Jenkinson, one of Brianna's two killers who according to the judge in the case was the ringleader.

Esther Ghey is campaigning for restrictions on what under-16s can access on their cell phones and for the wider use of mindfulness in schools, as a way to help teachers and children to look after their mental health.

At the end of Sunak's weekly — and often rowdy — questioning in Parliament, he acknowledged the presence of Brianna's mother in the chamber.

"If I could just say also to Brianna Ghey's mother who is here, as I said earlier this week, what happened was an unspeakable and shocking tragedy,” he said. “As I said earlier this week, in the face of that, for her mother to demonstrate the compassion and empathy that she did last weekend, I thought demonstrated the very best of humanity in the face of seeing the very worst of humanity.

“She deserves all our admiration and praise for that," he added. Stonewall, a group that stands for LGBTQ+ rights, urged Sunak to apologize for his “cheap, callous and crass” use of trans people as a “punchline.”

The exchange has stoked concerns about the level of debate in the run-up to a general election later this year. With his Conservative Party trailing the main opposition Labour Party heavily in the opinion polls, Sunak has come under pressure from some of his own lawmakers to put so-called “culture war” issues on the agenda, in an attempt to create dividing lines that could begin to dominate the public debate.