Author and commentator Matt Walsh says as discovered in his documentary, 'What is a Woman?', gender ideologues "certainly cannot define the term".

"It starts with just recognising that gender ideology is this pervasive, toxic influence in our culture across the world, across the western world anyway" Mr Walsh told Sky News host Rita Panahi.

"And also realising that in spite of the fact it's been so successful in claiming so many people's minds, it is really quite hollow at its core."

He said just a couple of questions "really bring down the whole house of cards", starting with the question he poses in his documentary: "what is a woman?".