David Cameron is facing demands for an apology after telling a female shadow cabinet minister to "calm down, dear" in furious exchanges at Prime Minister's Questions.
Labour branded the jibe, aimed at shadow Treasury chief secretary Angela Eagle, as "patronising, sexist, insulting and un-prime ministerial".
But No 10 aides brushed off opposition demands for an apology, insisting it was clearly a humorous remark - echoing a well-known car insurance advert starring Michael Winner.
Mr Cameron's comment came as he defended his Government's plans to reform the NHS, which he said were even backed by former Labour MP Howard Stoate, a practising GP.
Ms Eagle, seated on the Labour front benches, loudly retorted that Dr Stoate had stood down at last year's election, rather than being defeated as the Prime Minister claimed.
Mr Cameron turned to her and said: "Calm down, dear, calm down. Calm down and listen to the doctor," prompting the Labour benches to erupt in outrage, with party leader Ed Miliband appearing to demand an apology.
The Prime Minister, however, pressed on telling them: "I said calm down, calm down dear. I'll say it to you if you like... I'm not going to apologise. You do need to calm down."
Afterwards, Ms Eagle suggested that Mr Cameron was out of step with modern times, although she stopped short of calling for an apology.
"I don't think any modern man would have expressed himself in that way," she said.
"I think if there is an apology to make, it should be for the dreadful growth figures we have seen today, which demonstrated that the economy has effectively flatlined for six months."