It came after a cabinet minister said the prime minister should “reflect” on his behaviour and attitude towards trans people.
Sunak triggered a widespread backlash, including from Tory MPs, for the remark during a clash with Keir Starmer at PMQs on Wednesday.
Attacking Starmer for repeatedly changing his policy positions, the prime minister said this included “defining a woman”.
He added with a laugh: “Although in fairness that was only 99% of a U-turn.”
It was a reference to the Labour leader’s previous comment that 99.9% of women “haven’t got a penis”.
Brianna Ghey’s father, Peter Spooner, condemned Sunak’s “absolutely dehumanising” joke and called on him to apologise.
But asked by broadcasters this morning if he would say sorry, Sunak refused.
“If you look at what I said, I was very clear, talking about Keir Starmer’s proven track record of U-turns on major policies because he doesn’t have a plan,” he said.
The prime minister claimed it was actually the Labour leader - who sharply criticised Sunak for the joke - who was in the wrong.
“To use that tragedy to detract from the very separate and clear point I was making about Keir Starmer’s proven track record of multiple U-turns on major policies, because he doesn’t have a plan, I think is both sad and wrong, and it demonstrates the worst of politics.”
Last week two 16-year-olds were convicted of murdering Brianna , who was transgender.
Earlier this morning, Cabinet minister Penny Mordaunt, the Commons leader, appeared to criticise Sunak in public.
Speaking in parliament, she said: “Whatever the pressures and mistakes that are made in the heat of political combat we owe it to the people who sent us here to strive every day to make them proud of us and this place.
“The prime minister is a good and caring man. I am sure that he has reflected on things.
“And that is not just about Mr and Mrs Ghey that he should reflect on, but I am sure he is also reflecting on people who are trans or who have trans loved ones and family, some of whom sit on these Green benches.”
Other Tory ministers have struggled in interviews to explain away Sunak’s comment following the backlash.
Policing minister Chris Philp claimed on the BBC that the PM “wasn’t talking about trans issues”.
Laura Trott, the chief secretary to the Treasury and close ally of Sunak, told LBC that his comment was “not a joke” - despite him having delivered it as a punch line with a laugh.