Nick Xenophon has confirmed he holds dual British citizenship and may not be eligible to sit in Parliament, becoming the seventh MP whose position has fallen under a cloud.

Though born in Adelaide, Senator Xenophon's father Theo was born in Cyprus, which remained a British colony until 1960. He migrated to Australia in 1950, where Senator Xenophon was born.

Travel documents show Theo came to Australia on a British passport. As a result the UK considers him a "British overseas citizen", a class of citizenship that confers few rights on the holder.

Senator Xenophon said the citizenship category was "useless" except to his "political opponents" who he said had worked hard to use it to remove him of Parliament.