High Court ruling stokes citizenship saga

Four MPs will resign and face by-elections after the High Court's decision to rule Labor senator Katy Gallagher ineligible due to dual citizenship.

Rebekha Sharkie has resigned from parliament in the wake of a High Court ruling. (AAP)

CITIZENSHIP SAGA SPARKS BY-ELECTION BONANZA

LABOR

* Susan Lamb (Longman, Queensland, margin +0.8%)

Acquired British citizenship by descent through her Scottish-born father. She attempted to have it renounced but her application was refused on August 10, 2016. The government will fancy their chances in a by-election in Lamb's Queensland seat of Longman, where Labor have a razor-thin margin of less than one per cent.

* Justine Keay (Braddon, Tasmania, +2.2%)

Keay acquired British citizenship through her father, but citizenship renunciation from UK Home Office was dated July 8, 2016. Former independent senator Jacqui Lambie has ruled out a tilt in the Tasmanian marginal seat.

* Josh Wilson (Fremantle, WA, +7.5%)

Born in Britain but citizenship renunciation from UK Home Office was dated June 24, 2016. Has a healthy margin in Fremantle, the seat of former Labor prime minister John Curtin.

CROSS BENCH

* Rebekha Sharkie (Mayo, SA, +3.2-5.5%)

Born in the UK. Renounced UK citizenship on April 19, 2016 but renunciation was registered with the UK Home Office on June 29, 2016. The Liberal Party will zero in on Sharkie's Adelaide seat of Mayo, which she won from former Liberal minister Jamie Briggs. After South Australia's recent distribution, ABC election expert Antony Green puts Sharkie's notional margin over the Liberals at 5.5 per cent and Labor at 3.2 per cent.