Jacqui Lambie’s defection from the Palmer United Party was the culmination of months of mounting tensions between the Tasmanian Senator and party leader Clive Palmer. In the past month, she was demoted from her position within the party and prevented from attending party room meetings.

Lambie had been voting against the party’s wishes on legislation on Australian Defence Force pay and financial advice. At the start of the month she said she didn’t care about Palmer’s position on the matter.

But her decision to become an independent raises a tricky parliamentary question: given that most people vote above the line on the Senate ballot paper, does a seat belong to an individual or a party?

Is there any precedent?

The most recent federal defection occurred in September, when Senator John Madigan quit the Democratic Labour Party and now holds the seat as an independent. The Democratic Labour Party is currently launching proceedings in the High Court to take the seat back from him.

In 2002, then-Democrats leader Meg Lees had a public falling-out with her deputy, Natasha Stott-Despoja. Lees ended up quitting the Democrats and sitting as an independent senator.

Does an MP ever have to give his or her seat back to a party?

When Lees left the Democrats, the leadership used the party’s constitution to argue that she must also vacate her seat. But Lees felt no need to follow the constitution of a party that she didn’t belong to.

However, the DLP is citing Australia’s constitution in the party’s bid to retain Madigan’s seat. Although the party’s interpretation of the legislation is debatable, Australia’s constitution is more relevant to Madigan than the Democrats’ own constitution was to Lees.

What does the constitution say?

Australia does not have an anti-defection law or anything else to oblige senators who become independent to give up their seats. However, the DLP argues that they should be allowed to replace Madigan under section 15 of the constitution, which relates to a Senate seat becoming “vacant” before the senator’s term of service has expired.

DLP president Paul Funnell says his party believes that Madigan’s departure from the DLP means that his seat is now vacant, and this is the argument the party wants to put to the High Court.

In the event of a vacant seat, the house can choose his or her replacement. Section 15 goes on to say that if the representative was endorsed by a political party when he or she was elected, the person who replaces the MP must be a member of the same party.

Why isn’t there a law specifically for defection?

It has been discussed before. A research paper by Sarah Miskin in 2002 outlined the arguments for and against creating a law to stop elected representatives from defecting.

On the one side is the argument put forward by the DLP, which is that Victorians did not vote for Madigan, but for the party he represented. Proponents of this reading may have a point. In the Senate, most Australians vote above the line and therefore vote for the party, not the person. But given the complicated way that preferences are distributed, there are holes in that argument too.

Miskin’s paper said that an anti-defection law would “ensure the will of the people as expressed in a democratic election is upheld”.

On the other hand, Miskin noted that a law outlawing defecting from a political party would also be problematic. Doing so would limit a senator’s ability to act according to his or her conscience and potentially impinge on rights to freedom of association. Such a law would also give parties much more power, which might be unconstitutional.

What happens now?

It’s hard to say. Although elected representatives defecting from their parties to serve as independents is nothing new, this particular piece of legislation has never been tested. If the DLP is successful in its bid to reclaim Madigan’s seat, all eyes will turn to Clive Palmer (just for a change). Although he’s been saying that Lambie is just one senator, it would be surprising if he didn’t take an opportunity to reclaim her seat.

However, constitutional law expert George Williams of the University of New South Wales has expressed doubts. He says it would be “very difficult” for the DLP to convince the High Court that Madigan’s seat is now vacant.

The Conversation’s Michelle Grattan also weighed in, saying that the DLP would be really “whistling in the wind to try and get that seat back”.

If Madigan and Lambie retain their seats, it dramatically changes the power structure in the senate. While Madigan was not formerly the member of a voting bloc, Lambie will certainly have more power to negotiate on her own terms than she did as a member of PUP.