The two politicians elected to represent the entire South East region of South Australia are starting the year in custody.

That's nearly 50,000 voters — living across an area roughly the size of the Netherlands — whose elected member of state parliament is detained.

And in three months' time, half of those voters might be asked to cast their ballot for an MP who has restrictions on his ability to leave home. 

How on earth did we get here?

The story of Bell and McBride

The two men at the centre of this story, MacKillop MP Nick McBride and former Mount Gambier MP Troy Bell, are in cells for unrelated reasons.

Mr McBride was arrested by police over the weekend and charged with the aggravated assault of his wife and breach of bail.  

Nick McBride's electorate includes South East towns like Robe, Bordertown, Kingston SE, Millicent, Naracoorte and Penola. (Supplied: Nick McBride)

His lawyers told the court the charges would be "vigorously defended".

He remains in custody until at least January 6 and is only eligible for home detention bail (more on that later).

Bell on the other hand is two months into a five-year prison sentence for stealing more than $430,000 in public money meant for not-for-profit education organisations.

He resigned from parliament in September, a month before he was sentenced, and Mount Gambier remains without an MP after the House Speaker opted against holding a by-election.

Troy Bell remained in parliament for eight years despite a serious legal cloud over his future. (ABC News: Daniel Taylor)

While their legal situations are different, Bell and Mr McBride's political careers share some striking similarities.

Both were elected as Liberals in South East seats — Bell in 2014 and Mr McBride in 2018.

Both later resigned from the party to stand as independents — Bell for legal reasons and Mr McBride due to his dissatisfaction with the party.

Both also caused plenty of political headaches for their former party — be it through public criticism, crossing the floor, or courting Labor investment in the South East.

Both have strong local profiles and support from their electorates.

And both have gotten into significant legal trouble.

McBride's next move

But significant legal trouble does not necessarily mean losing your seat immediately, if Bell's career is anything to go by.

Out on bail with serious charges hanging over his head, Bell went to the voters of Mount Gambier and asked to be re-elected as an independent. They obliged, twice.

Could Mr McBride pull off the same feat in MacKillop?

Possibly, but he might have to do it while stuck on home detention bail.

This hurdle to his re-election bid only became clear during his court appearance on Monday.

It even seemed to catch his lawyer by surprise.

Jane Abbey KC had applied to free Mr McBride on a standard bail agreement, before the magistrate informed her that parliament recently tightened the bail act.

Those changes, which passed with bi-partisan support last year, meant that due to the allegations against Mr McBride, he was only eligible for home detention bail — a fact later conceded by Ms Abbey.

Mr McBride is yet to declare whether this changes his intention to run for re-election, but it's clear his Liberal opponents think it should.

"It's almost impossible to see how he can do his job from a jail cell," Liberal Party leader Ashton Hurn said on Tuesday.

"I mean clearly there's a lot to play out in the courts, but I'm almost certain that he'd be contemplating resigning, and if he's not then he should."

Winning from home

Nick McBride's bid to stay in parliament has been complicated by his legal case. (Supplied: SA Parliament)

The conditions of Mr McBride's home detention bail — including what exemptions he may or may not get for work — are not clear yet.

That is, of course, if he is granted bail at all.

And it’s fair to say examples of successful political campaigns while a candidate is detained are few and far between.

The Irish Republican Army's Bobby Sands famously pulled it off in 1981, winning a seat in the UK Parliament while on a hunger strike in a prison near Belfast.

There's also a handful of recent bizarre examples in the United States.

This includes a Washington DC prisoner who won a local government position overseeing his jail, and a Virginia state lawmaker who won re-election while serving a six-month sentence for an alleged sexual relationship with his underage secretary.

In most cases, however, detention makes the task of winning office a whole lot harder.

"Obviously, [Mr McBride's] not going to be able to go to all the local community events in all the different towns he represents if he's on home detention," said Josh Sunman, associate lecturer in politics and public policy at Flinders University.

"It's not necessarily a case of this means he can't win, but I certainly don't think it's helpful."

A glimmer of Liberal hope?

For the Liberals to maintain their 13 seats in the lower house, they may have to win back MacKillop and Mount Gambier to offset losses they fear they will suffer to Labor in metropolitan Adelaide. 

The party has talked up its efforts to run stronger campaigns in these seats, preselecting its candidates for the South East back in August.

And the McBride news has given Ashton Hurn another chance to spruik the party's "extraordinarily well-connected" candidate for MacKillop, Rebekah Rosser — a Robe local, lawyer and public relations professional.

The Liberal Party has picked candidates Lamorna Alexander (left) and Rebekah Rosser (right) to take back Mount Gambier and MacKillop respectively. (ABC South East SA: Eugene Boisvert)

"I think the people of the South East want a … strong representative who's going to be out in the community working hard for them each and every day," Ms Hurn said.

"And of course in Nick's circumstances currently that makes it pretty difficult for him."

The Liberal Party in SA has copped its share of political humiliations over the past four years, but failing to defeat an opponent on home detention would have to rank pretty highly.

In the meantime, residents in the South East could be forgiven for feeling a bit bewildered by a chain of events that has led to both of the MPs they elected four years ago currently sitting in custody.