One Nation senator Malcolm Roberts is fighting for political survival after Pauline Hanson averted an embarrassing defeat in the Senate by personally referring his "complex" dual citizenship case to the High Court.

Despite insisting for weeks that Senator Roberts properly renounced his British citizenship before the last election, Senator Hanson moved the Senate motion after it became clear a Greens-led push against him would succeed.

Richard Di Natale's motion had the support of Labor, the Nick Xenophon Team and other key crossbenchers. Senator Hanson's eleventh hour intervention ensured the motion passed without a potentially damaging debate.

The referral caps a turbulent three weeks for Senator Roberts, who has been refusing to answer key questions about his citizenship history or produce documents that he says proves he is eligible to remain in the Senate. Section 44 of the constitution prohibits dual citizens from serving in Federal Parliament.