Abbott dares Shorten on UK citizenship

Tony Abbott has challenged Labor leader Bill Shorten to prove he isn't a dual citizen by releasing documentary evidence from British authorities.

"I say to Bill Shorten show it or shut up," the former prime minister told reporters in Canberra on Monday as he brandished a letter from the British government showing he renounced UK citizenship in 1993.

"I say that he should just be straight with the Australian people about his citizenship."

Mr Abbott claimed the opposition leader was in exactly the same situation as Deputy Prime Minister Barnaby Joyce, who renounced his New Zealand citizenship by descent from his father.

"Bill Shorten has claimed he has renounced his British citizenship but he's never proven it," Mr Abbott said.