Two green bottles and up to four blue ones. Falling from the parliamentary wall, unless the High Court saves them from the rules about MP qualifications. The six are now-resigned Greens senators Scott Ludlam and Larissa Waters, fellow upper house members Matt Canavan (LNP) and Malcolm Roberts (One Nation), and two government members of the lower house, Barnaby Joyce and David Gillespie (both Nationals).

At least that’s the latest count, as of Monday’s referral of Joyce to the court. I hesitate to file this piece lest the number rise again today.

What happens now?

First, a word on process. Gillespie’s case is different from the others, in two ways. He is not a dual citizen but faces claims about his “pecuniary interest” in a shop sub-leased to Australia Post. This is the constitutional rule that knocked out Family First senator Bob Day in April.

Also, Gillespie is being sued by his former Labor Party rival, acting as a “common informer” – a fancy term for an officious bystander who sues to enforce the law.

This avenue to challenge an MP has not been used before. It’s not entirely clear the court has power to declare Gillespie “not duly elected”. (As opposed to exacting a penalty from an MP, in the princely sum of A$200, for any day they sat while under a disqualification.)

The other five – facing dual citizenship claims – are not being sued at all. Rather, parliament has referred their positions to the court. A few things flow from that, aside from the Commonwealth almost certainly having to cover their legal costs.

One is that there is no belligerent plaintiff to argue against, say, Joyce. There will just be the solicitor-general, putting legal arguments for the Commonwealth, plus lawyers for whichever of the other four MPs or their parties choose to be represented.

Yet Joyce, Canavan and Roberts share a desire to convince the High Court that they are legitimate, arguing on related grounds that it might be unfair to unseat them.

Another is that while the election is long over, the High Court says it can undo an election on a reference from parliament. This is due to a quirky, 30-year-old ruling. I say quirky because, for more than a century, there’s been an absolutely strict time limit for challenging elections.

With electoral fraud, unlawful campaigning, or electoral commission stuff-up, a court case must begin within 40 days of the election. Yet the High Court says it can undo election results, long afterwards, over qualifications issues.

What will the MPs argue?

We must await the arguments, but it seems that Joyce, Canavan and Roberts will argue that they either took reasonable steps to renounce (Roberts) or that it was unreasonable to expect them to have known of their dual citizenship (Joyce and Canavan). In a 1992 case, the High Court softened the law against dual citizenship to allow a defence of “reasonable steps” of renunciation.

Roberts was born in India (after partition) to a Welsh father. He took some steps – three emails in one day on the eve of nominating, apparently – to renounce his UK inheritance. Was that enough, given the UK has a set application form and fee for renunciation? Roberts, some time after the election, received notice that his UK citizenship was expunged.

Canavan, Australian-born, asserts that his mother took out Italian citizenship on his behalf, without his knowledge.

Similarly, Joyce, also Australian-born, says he was blindsided to learn he had New Zealand citizenship via his NZ-born father. They want the court to inject a subjective element – actual or constructive knowledge of dual nationality – to avoid a finding that taking no steps to renounce does not meet the idea of “reasonable steps”.

It’s possible Joyce will also argue the details of NZ law. For example, whether it automatically bestowed citizenship on him, or whether he was merely guaranteed it if he applied to activate it.

The Greens pair, by resigning, seemed to admit they were disqualified. But MPs cannot declare themselves improperly elected. Only the court can do that.

Ludlam (New Zealand) and Waters (Canada) were each born overseas, but to Australian parents. They left their birth countries at the tender ages of three years and 11 months respectively.

At least in Waters’ case, her family lore (not law) was that her nationalisation as an Australian toddler terminated any Canadian status. In some countries, you lose your birth citizenship when you take out another nationality. This was the law in Australia until recently.

The logic of the Greens’ political position is to have their two Senate seats filled ASAP. Yet, in substance, their pair are hardly more blameworthy than the other MPs, who seek to fight on. They have hemmed themselves in, however, by resigning.

If the court found their disqualifications were OK, the Greens could reappoint them or any other Greens member, under the old rule for filling a “casual vacancy”.

Finally, to legal consequences. If a senator is declared “unduly elected”, the Australian Electoral Commission conducts a recount. Invariably, the next candidate in the party’s original electoral ticket inherits the seat.

That windfall beneficiary can keep it, or the party could cajole them to resign in favour of … the unelected MP. Because all of these MPs, with sufficient paperwork and knowledge, can fix up their qualifications.

Roberts and Waters say they’ve done that. Joyce and doubtless Canavan have that in train.

In a lower house seat, however, a recount would be crazy. The seat would go to the rival major party, robbing the electorate. Instead, the court effectively triggers a byelection.

In a worst-case scenario for Joyce (or Gillespie), he would recontest that fresh election. A lot would be at stake in New England (or Port Macquarie). But it’s hard to see the electors there treating now-ex-Kiwi Joyce as a fifth columnist.

The law is an unnecessary mess

All this is a law professor’s picnic.

Section 44, as it applies to elections, detracts from, rather than adds to, democracy. Its technicalities are a thicket, catching many a candidate. It sits oddly in a Constitution that never guaranteed a right to vote, leaving that small matter to the national parliament.

It’s time for reform. We inherited the dual citizenship rule, an old rule about fealty to one Crown, from our English forebears.

The founders struck it in stone in the Constitution. Yet state parliaments are fine with dual citizens being elected. So too is New Zealand. And, funnily enough, so nowadays is the UK.