A male MP from New Zealand’s opposition party who called the prime minister, Jacinda Ardern, a “stupid little girl” remains unidentified more than a week after making the remark in parliament.

A search of parliamentary records and an investigation by Newshub have so far not uncovered the identity of the man who blasted Ardern – the third woman to lead the country. The speaker of the house, Trevor Mallard, halted proceedings immediately after the comment was made, and demanded the man apologise for the “very sexist remark” directed towards the prime minister, who is 37 years old and expecting her first child next month.

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The MP who spoke the words has yet to own up to the incident. In doing so, he would have to issue an official apology to Ardern and withdraw the remark. According to comments made by Mallard at the time, the MP was sat somewhere behind the opposition leader, Simon Bridges. Newshub approached 10 MPs from the New Zealand National party who could have made the remark and all denied it had come from them.

Bridges said he would be reviewing footage of the incident to identify who had spoken, and that if the culprit was identified he would consider what consequences the MP would face. “Parliament’s a place of cut and thrust. People say things in the heat of moment, on all sides of the house, including, let’s be honest, the speaker,” Bridges told Newshub.

The minister for women, Julie Anne Genter, said the remark was unacceptable. “People should get with the times, especially the National party backbenches. Grow up,” she said.

