Malcolm Turnbull has conceded there might be more by-elections to deal with ineligible MPs.

That gets the hearts racing among the political class. But does it mean ordinary voters should be factoring in a visit to the polls on a Saturday soon?

Let's look at how close we could be to another election.

Where and when are people going to have to vote next?

The people of Bennelong in Sydney's west appear most likely because their MP, Liberal John Alexander, might be a dual citizen by descent.

Mr Alexander has not renounced British citizenship, so he would be a dual citizen unless his UK-born father gave it up before he was born. That part's unclear.

(FYI: His dad only had two years in which to do this. The junior Alexander says his father did renounce as soon as he could, but we haven't seen any evidence of that yet.)

Malcolm Turnbull says anyone who believes they are a dual citizen and could be ineligible to sit in Parliament should resign. That puts the pressure on all MPs to recheck their status.

If there are resignations this week, then there is potential for more by-elections by the end of the year, most likely on December 16.

Questions persist about the citizenship of many other MPs, making it possible there could be several by-elections.

How many by-elections before they're in real trouble?

Three would be pushing it. Let's count. (Remember, the Coalition needs half of the 150 House of Representatives seats plus one to form a majority government. That's 76. We're going to focus on the Coalition-Labor numbers, because they're the ones who could form government.)

There's one by-election already underway — in New England, voters are heading back to the polls on December 2 because Barnaby Joyce was a dual citizen when he was elected.

That has temporarily stripped the Government of its one-seat majority, but with the confidence of cross-bencher Cathy McGowan and the Speaker's casting vote, it remains confident.

Cathy McGowan has offered her supply and confidence to the Government. ( ABC News )

So they're at 75-69, plus Ms McGowan. Sweet.

New England is a safe seat where Mr Joyce will likely win, restoring the Government's one-seat majority.

That brings them back to 76-69.

But other by-elections would not be so smooth for the Government.

Bennelong would be a test. Mr Alexander held the seat comfortably last year. It has been a long-term Liberal seat, but Labor's Maxine McKew defeated then-prime minister John Howard in 2007, before losing to Mr Alexander three years later.

A Bennelong by-election creates the possibility of the Government getting its one-seat majority back after the New England by-election and then losing it a fortnight later, thus returning to the more precarious situation of relying on Ms McGowan.

Back to 75-70 if Labor was to win that seat (or 75-69 if it went to someone else). Assuming that they'd still have Ms McGowan's support, the Coalition are probably still OK in this scenario.

Trouble would come if there were any further by-elections for the string of seats where there are questions over MPs' eligibility — especially if they are marginal electorates.

If the Government drops below 75 seats we're back in hung parliament territory, where neither major party has enough seats to govern in its own right, so they need to make deals with the crossbench to pass legislation.

If this is ringing a bell, it's because that's where the Gillard government ended up at the 2010 election.

But MPs on both sides have citizenship queries, so it is possible there could be contests in a range of seats around the country to determine if the Government can hold its majority.

Do we all have to vote again?

We're getting deep into hypothetical land here. But the Government *might* decide to hold a full Lower House election instead of a string of by-elections.

The prospect of a series of MPs being ineligible would create intense pressure on the already fragile Government.

The Prime Minister could choose to try to restore stability with an election for the House of Representatives instead.

"Do the unthinkable and put it all on the table" was the phrasing of one Labor figure.

But Mr Turnbull's last big political gamble was for a double-dissolution, and that has not been as successful as he had hoped.

It would be an unorthodox move, because the timing means he could not hold a normal election where voters elect all the House of Representatives members and half the senators.

It would have to only be for the Lower House with a subsequent half-Senate election only possible from July next year.

The last House-only election was in 1972, spookily on December 2, the date of the New England by-election.

Stay tuned.