Peta Credlin has unequivocally denied she was having an affair with former prime minister Tony Abbott, rejecting the rumours as "completely false" and "utterly untrue."

Ms Credlin, who served as Mr Abbott's chief of staff, has penned an opinion piece for News Corp, to address the controversial new book by political commentator and former Howard government staffer Niki Savva which reveals the dysfunction of the former prime minister's office.

Road to Ruin does not allege an affair between Ms Credlin and the former prime minster. But it does quote one unnamed Liberal who says they witnessed Ms Credlin feeding Mr Abbott food from her fork in public at a restaurant and resting her head on his shoulder. And it cites an anonymous minister who says he saw Mr Abbott slap Ms Credlin on the bottom not knowing he was watching the scene.