Martell said she had told people in the past about the incident, but no one believed her. That is why she hadn't come forward until now, she said.
"I was only young and you don't run around saying, 'Rolf Harris did this' or 'I saw this' because nobody's going to believe you," she said.
"It's quite scary when you're 19, 20, you're a Kiwi backpacker, and you're in a London studio with people like this and you see what you see."
Scotland Yard police interviewed Martell in the presence of an Australian Federal Police detective.
It is understood two other women would be interviewed as part of Operation Yewtree, which was launched in the wake of the Jimmy Savile case.
The claims against Harris and Savile are not related, but are being investigated by the same taskforce.
- nzherald.co.nz