The High Court has ruled that Labor Senator Katy Gallagher isn't eligible to serve because she didn't renounce her British citizenship in time for the 2016 election.  Four other MPs stood down because of the decision.

Rebekha Sharkie of the Centre Alliance (formerly the Nick Xenophon Team) realized the ruling could apply to her and stood down, requiring a by-election in Mayo; Labor's Josh Wilson, Susan Lamb, and Justine Keay also resigned, triggering  by-elections in Fremantle, Longman, and Braddon, respectively.

Labor senator Katy Gallagher insisted she had taken all reasonable steps to renounce her British citizenship, but the UK Home Office did not register her renunciation until August.  That was more than a month after the 2016 federal poll.

She issued a statement and apologized to constituents:  "To the people of the ACT, I'm very sorry that this disruption has occurred to one of your federal representatives.

"To have my place in the Senate end like this today is very deeply disappointing, but I believe that I have more to contribute to public life," she wrote, "I will take the time to talk with Labor Party members on how I can do this over the months ahead."

The High Court ordered that a special recount be held.  Since union leader David Smith was the next candidate on the Labor Senate ticket, he will likely be next in line to fill the vacancy;  Mr. Smith told the ABC he would not vacate the seat to allow Ms. Gallagher to run for it again.