A prominent UK columnist has accused Jacinda Ardern of betraying voters following her pregnancy news.

Liz Jones, for the Mail on Sunday, slated Ardern's comments about "wearing two hats" as Prime Minister and now a mother.

"Oh please! Giving birth months after winning an election isn't multi-tasking," she wrote.

"It's more a betrayal of voters. It's worse than Damian Green and those porngate claims! At least he could snap his laptop shut if World War III broke out. What will a new mum PM do? Hurry back from [the supermarket], wailing: 'I'm sorry I missed Armageddon, but we'd run out of organic Ella's Kitchen'?"

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She also took a shot at Ardern's comment about how in June her "team will expand from two to three".

"Yuk! Even I've now got morning sickness. They're not a team. What's baby going to be? Minister for Midday Naps?" Jones wrote.

"I know the old argument: surely being a mum makes you more rounded, empathetic. Isn't it all about work/life balance these days?

"Fine, if you want to work behind the counter at Boots. But if you want to get to the top of your game? If you want to be a world leader? Surely your country shouldn't have to compete for your attention with a colicky toddler."

Ardern announced her pregnancy on Friday via Instagram.

She discovered she was pregnant just six days before she became Prime Minister-elect. Winston Peters announced NZ First would form a coalition with Labour on October 19.

Jones in 2012 was named Columnist of the Year at the British Society of Magazine Editors Awards.

She's known for her confessional and controversial columns. Among her digs at others, she has called Rihanna a "poisonous pop princess", and said BBC TV presenter Clare Balding had a "cheap hat and shoes" and "sense of superiority".

Jones continued her Sunday column tirade by slamming an editorial by Vogue's new beauty director, Jessica Dinerm, who said that it was "game-face on" when she "leaves her 2-year-old son with her nanny".

"Can I tell you the truth about sitting opposite one of these new mums?" Jones write.

"Game face? Effective? They crawl into work late, with egg in their hair and wearing last night's onesie. They are never, ever off the phone, microscopically grilling the nanny/granny about what the blasted child is eating, becoming enraged if water is given from anything plastic ('It must be glass! Glass!!') while simultaneously cooing at baby's Instagram feed.

"Once they get off the phone to the nanny/granny, they are then back on it again, discussing the new leather flooring in the master bedroom ('So good for tiny knees once he starts crawling'), and arranging a villa in the South of France.

"Then they try to get hold of the other member of the 'team' triangle, Dad, whose colleagues at his investment bank have absolutely no idea he is even attached, let alone a new parent."

The couple talk about their pregnancy at a press conference outside their home on Friday. Photo / Greg Bowker
The couple talk about their pregnancy at a press conference outside their home on Friday. Photo / Greg Bowker

She said it made her mad when women "wailed" about being paid less than men because it had nothing to do with discrimination. It was because while women were on maternity leave, you never heard from them except when they came into the office to collect their gifts.

"When my fashion director disappeared on maternity leave, I had to call to let her know we were still, you know, being published every month. When she returned to work three days a week (you see?), it was barely a season before she announced she was off to breed another one.

"When I objected she said: 'But it's a feminist magazine! This is what we stand for!' I countered: 'But you've just increased my workload and blown my budget. I'm a woman as well, you know.' 'Barely,' she muttered, gathering her things."