The Prime Minister joked about his floundering opposite number as he sought to rally his backbenchers. He made the remarks at a dinner held for Tory MPs at the Park Plaza hotel in Westminster.
After two years of living through the pandemic, the gathering was the first time all Conservative MPs had held a bonding event since the 2019 election.
And seeking to unite the troops after a year that has seen Covid rules and partygate rows test relations, Mr Johnson took aim at Sir Keir as he addressed the room.
Opening his speech, he said: “Good evening ladies and gentleman.
“Or, as Keir Starmer would put it, people who are assigned female or male at birth.”
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Sir Keir replied: “No, no, no.
“It’s just, I don’t think that discussing this issue in this way helps anyone in the long-run.
“What I want to see is a reform of the law as it is, but I also am an advocate of safe spaces for women.”
He added: “Anybody who genuinely wants to find a way through this, I want to discuss that with.
“I do find that too many people – in my view – retreat or hold a position of which is intolerant of others.
“And that’s not picking on any individual at all, but I don’t like intolerance, I like open discussion.”
In contrast to the Labour leader’s dodging of the question, Mr Johnson has tackled the issue head-on.
The Prime Minister’s official spokesman said trans people should be treated with “maximum possible generosity and respect”, but Britain must not ignore “basic facts of biology”.