Prime Minister Jacinda Ardern has sacked Iain Lees-Galloway as a minister over an inappropriate relationship he had with a staff member in one of the departments he headed. The relationship lasted 12 months and has cost Lees-Galloway his political career - he will not contest September's election. Lees-Galloway, 41, is married with three children. He said he had "acted completely inappropriately in my position and cannot continue as a minister". Ardern said ministers having affairs was not necessarily inappropriate behaviour, and it depended on each individual circumstance. But Lees-Galloway's position was untenable because he was the Minister for Workplace Relations and Safety, and he had opened himself up to accusations of improperly using his power. "He has not modelled the behaviour I expect as a minister in charge of setting a standard and culture in workplaces," Ardern said. The Prime Minister did not want to identify the woman involved, but added that she wasn't an intern. Asked about whether it was now open season on MPs' affairs, she said the compelling factor was the perception of the inappropriate use of his ministerial position, in particular the Workplace and Safety portfolio. Ardern wouldn't be drawn on whether affairs were automatically conduct unbecoming of a minister, saying that she would deal with each particular circumstance. "At any point where I have things that concern me, I deal with them in an appropriate way, but I don't want to be drawn into hypotheticals or rumours without substance." Whether Lees-Galloway had other affairs was immaterial, she said.